Made available through Montana State University’s ScholarWorks Evaluation of the bonding properties between low-value plastic fibers treated with microbially-induced calcium carbonate precipitation and cement mortar Michael Espinal, Seth Kane, Cecily Ryan, Adrienne Phillips, Chelsea Heveran © This manuscript version is made available under the CC-BY-NC-ND 4.0 license https:// creativecommons.org/licenses/by-nc-nd/4.0/ 1 Evaluation of the bonding properties between low-value plastic fibers treated with 2 microbially-induced calcium carbonate precipitation and cement mortar 3 4 Michael Espinal1,2, Seth Kane1,2, Cecily Ryan1,2, Adrienne Phillips2,3, Chelsea Heveran1,2 5 1 Mechanical and Industrial Engineering Department, Montana State University, 6 Bozeman, MT 59717, USA; 7 michael.espinal@student.montana.edu (M.E.); sethkane@montana.edu (S.K.); 8 cecily.ryan@montana.edu (C.R.); chelsea.heveran@montana.edu (C.H.) 9 2 Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, USA; 10 adrienne.phillips@montana.edu (A.P.) 11 3Civil Engineering Department, Montana State University, Bozeman, MT 59717, USA 12 13 Abstract 14 Plastic fiber reinforced cementitious materials offer the potential to increase the reusability of 15 plastic waste and create lower-CO2 cementitious composites. However, the bonding properties 16 of many plastic types with ordinary Portland cement (OPC) are largely unknown. This work 17 employs single fiber pullout (SFPO) tests to quantify the interfacial bonding properties of 18 polyvinyl chloride, low-density polyethylene, polypropylene, polystyrene, and acrylonitrile 19 butadiene styrene embedded in OPC mortar. The interfacial bonding properties were compared 20 for fibers either treated with microbially-induced calcium carbonate precipitation (MICP) or left 21 untreated. SFPO tests revealed that plastic type had a large influence over bonding properties. 22 Specifically, the fiber surface energy, as estimated from water contact angle measurements, 23 was found to be the driving factor of bond strength. ABS had the highest surface energy and 24 demonstrated the strongest bonding out of all plastic types studied. However, MICP treatment of 25 fibers did not increase the interfacial bond strength for any of the plastics studied. The thick and 26 inconsistent coverage of biomineral over the fiber surface from MICP is likely attributed to 27 preventing an increase in bond strength. These results contribute to the design and application 28 of plastic-reinforced mortars by comparing bonding properties for a range of typically low-value, 29 unrecycled plastic types. 30 Keywords: Biomineralization, microbially-induced calcium carbonate precipitation, fiber 31 reinforced mortar, bond strength, waste plastic 32 1. Introduction 33 Ignited by the threat of climate change, researchers have been developing ways to 34 reduce the carbon dioxide (CO2) emissions from the production of concrete. Production of 35 ordinary Portland cement (OPC), the binding material in standard concrete, is responsible for 36 between 5-8% of anthropogenic global CO2 emissions [1,2]. A promising strategy towards 37 mitigating these impacts is to replace a portion of the OPC with a waste or low carbon footprint 38 material. 39 To date, most partial replacements of OPC are from industry by-products, such as fly 40 ash and blast furnace slag [1,3]. Waste plastics are another candidate to replace a portion of 41 OPC, since plastic fibers can serve as a reinforcing material [3]. Polyvinyl chloride (PVC, type 42 3), low-density polyethylene (LDPE, type 4), polypropylene (PP, type 5), polystyrene (PS, type 43 6), and acrylonitrile butadiene styrene (ABS, type 7) may be candidates for waste plastics in 44 fiber-reinforced cementitious materials. Currently, these low-value, challenging-to-recycle 45 plastics are typically landfilled, incinerated, or accumulate in the environment [4,5]. When 46 utilized in cementitious composites, plastic waste is typically added as a pure reinforcement 47 (i.e., does not a reduce the amount of OPC binder) [6–8] or replacement of aggregate [9–15]. 48 While these additions of plastics succeed at repurposing plastic waste, a partial replacement of 49 the OPC with plastic has the potential to further improve the sustainability of the cementitious 50 material [16]. 51 A challenge with the incorporation of plastic fibers into cementitious materials is that their 52 usage decreases the compressive strength of the composite [12–15,17–19]. Previous efforts 53 with using plastic as a reinforcement have utilized very small additions of plastic (e.g., < 2%) 54 [6,17]. When greater additions are used, larger decreases in strength are seen [12–15,17,18]. 55 For instance, Wang et. al [15] showed that including recycled high impact polystyrene at a 50% 56 volume replacement of sand led to a 49% reduction in strength compared to a 12% strength 57 reduction at a 10% replacement of sand in cement mortars. The reason for the reduction in 58 strength with the addition of recycled plastic can be attributed to poor interfacial bonding 59 between the plastic and cement [18]. Several surface treatments have been evaluated for their 60 potential to increase the bond between the plastic surface and mortar. These include chemical 61 [20–23], mechanical [21,24], plasma [25–29], and particle (biochar [8], silica [30–32], SiO2 [33], 62 calcium carbonate [16,34,35]) surface treatments. 63 Calcium carbonate (CaCO3) surface treatments stand out among other possible fiber 64 treatments due to the demonstrated ability of CaCO3 to repair cracks in concrete and seal leaky 65 oil wells [36,37]. The ability of CaCO3 to bond to the cement matrix, such as is required for 66 sealing cracks, suggests that CaCO3 could improve the interfacial bond between plastics and 67 cement, thereby strengthening the overall composite. In a previous research effort, Kane et al. 68 utilized microbially-induced calcium carbonate precipitation (MICP) to deposit a CaCO3 69 biomineral coating on plastic fibers. The treated fibers were then incorporated as a partial 70 cement binder replacement (1-5 wt.%) into plastic-reinforced mortar (PRM) [16]. MICP 71 treatment significantly increased the compressive strength of PRM containing PVC (18% 72 increase) but had limited impact on other plastic types. It was also found that PRM with MICP 73 treated mixed types 3-7 plastics had high compressive strength values (91% of the strength 74 measured in mortar specimens containing no plastic) [16]. The benefit to compressive strength 75 was greater for MICP than for enzyme-induced calcium carbonate precipitation using Jack Bean 76 meal as the enzyme source, suggesting that the microbial precipitation promotes stronger fiber 77 attachment to mortar [16]. However, the compressive strength of composites containing 78 individual plastic types 4-6 was not improved by MICP treatment, further motivating the need to 79 determine why MICP treatment improves composite strength for PRMs containing some plastics 80 but not others. 81 Single fiber pullout (SFPO) tests can be used to compare the bond strength between 82 different plastic types and cement and whether these bond strengths are improved by MICP 83 treatment. Most prior PRM and plastic-reinforced concrete (PRC) studies have considered PP 84 [8,20–23,31,32,34,35,38–41] or higher-value recyclable plastics such as polyethylene 85 [26,27,42]. Hao et. al [34] used SFPO tests to identify that PP’s bond strength with cement 86 mortar can be enhanced with certain ratios of mineral weight per weight of fiber. However, there 87 are important gaps in knowledge about how other common low-value waste plastics (e.g., 88 LDPE, PVC, ABS) bind to cement and whether these bond strengths benefit from MICP 89 treatment. Closing these gaps is crucial for optimizing PRM and PRC design as the interfacial 90 bond strength influences their mechanical properties [43]. 91 This study quantifies the interfacial bond strength, frictional bond strength, chemical 92 bond energy, and work to pullout of low-value plastics type 3, 4, 5, and 7 with and without MICP 93 treatment using SFPO testing. SFPO tests were also conducted on treated and untreated 94 plastic type 6 fibers, however the bonding parameters were not quantified. Because a prior 95 study by the authors determined that PRMs had different strengths depending on the type of 96 low-value plastic utilized (i.e., LDPE and PVC lowest, ABS and PS highest) [16], it was 97 hypothesized that bond strength would mirror these findings. It was further hypothesized that 98 calcium carbonate (CaCO3) biomineral from MICP would improve bonding between PVC and 99 mortar, since PVC composites showed the greatest strength benefit from MICP in prior work 100 [16]. 101 2. Materials and Methods 102 2.1. Plastic fibers 103 3D printer filament plastics were used to model common waste plastics. Polyvinyl 104 chloride (PVC), linear low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), 105 and acrylonitrile butadiene styrene (ABS) were cut to 50 ± 0.5 mm lengths for single fiber pullout 106 samples (Table 1). Fiber lengths were selected to ensure consistent embedment length 107 between trials and because similar lengths have been used in prior SFPO studies [24,40,44]. 108 The fibers were marked at 10 mm from the edge to act as a guide when manually embedding 109 into mortar. Fiber density was derived from the mass of individual fibers and the volume. Fiber 110 moduli were assessed through tensile testing using an Instron 5543. The loading rate was 5 111 mm/min and the distance between clamps was 30 mm. 112 113 Table 1: Properties of the plastic fibers. Measurements reported in mean ± standard deviation. 114 Fiber diameter was 1.75 mm for all plastic types. 115 Plastic Plastic Modulus Density Manufacturer Name Type Number (GPa) (g/cm3) PVC 3 Filamentum Vinyl 303 PVC - Black 1.29 ± 0.19 1.35 ± 0.02 LDPE 4 LLDPE108 Filament - Natural 0.16 ± 0.03 0.94 ± 0.01 PP 5 Centaur Polypropylene Filament - White 0.30 ± 0.02 0.89 ± 0.00 PS 6 NefilaTek 100% Recycled HIPS109 Filament - Black 0.65 ± 0.24 1.03 ± 0.00 ABS 7 NefilaTek 100% Recycled ABS Filament - Black 0.91 ± 0.27 1.04 ± 0.01 116 117 2.2. Biomineralization of plastic fibers 118 2.2.1. Microorganism and culturing conditions 119 The bacteria culture was grown from a frozen stock of S. pasteurii (ATCC 11859) in 100 120 ml of growth media (37 g/L brain heart infusion broth and 20 g/L urea) following a previously 121 established protocol [16]. The culture was grown in a shaking incubator at 150 RPM and 30˚C 122 for 24h. The parameters for the microbial solution followed those previously reported in Kane et 123 al. [16]. 124 2.2.2. Biomineralization of plastic fibers 125 Plastic fibers were coated with CaCO3 biomineral via MICP. During MICP, the microbial 126 urease of the S. pasteurii bacteria promotes calcium carbonate precipitation through urea 127 hydrolysis [37]. The biomineralization media consisted of 8 ml of S. pasteurii culture per 400 ml 128 of calcium mineralization media (3 g/L nutrient broth, 10 g/L ammonium chloride, 20 g/L urea, 129 and 49 g/L calcium chloride dihydrate) [16]. The S. pasteurii inoculum and calcium mineralizing 130 media were combined and stirred at approximately 400 RPM at room temperature. 131 Biomineralization began when the group of 13 fibers were submerged in the biomineralization 132 media for 48 hours using a mesh bag (EcoWear-Amazon) (Figure S.1). Thirteen plastic fibers 133 were mineralized per batch. The weight of each group of plastic fibers was recorded before and 134 after biomineralization, following the drying of fibers overnight at room temperature. The weight 135 was then divided by 13 to calculate the mean biomineral accumulated per fiber (Table S.1). 136 2.3. Fiber embedment in OPC mortar 137 The mortar consisted of ordinary Portland cement (OPC) type I/II (Quickrete), water, and 138 ASTM c778 graded sand as fine aggregate (U.S. Silica Company). Water:cement and 139 sand:cement mass ratios were 0.46 and 0.80, respectively. 140 OPC cement and water were mixed in a kitchenAide mixer on slow speed for 30 s 141 followed by another 30 s after adding the sand. The mortar was then mixed for 30 s on medium 142 speed followed by a rest period where the mixer was turned off for 90 s. During the first 15 s of 143 this break, the mortar stuck to the sides was scraped down into the bulk mortar. The mixer was 144 then turned on for a final 60 s on medium speed. The mixing protocol follows ASTM C305 [45]. 145 After mixing, 2”x 1 ¼” film canisters (Houseables-Amazon) molds were filled with mortar 146 using a procedure adapted from ASTM C192 standard [46]. Before filling, a line was marked 7 147 mm below the top to ensure the mold caps were flush to the mold. Each mold was then filled 148 half full of the fresh mortar. The mortar was tamped 25 times in a circular pattern (ensuring the 149 inside the mold was evenly rodded) using a 10 mm rod and tapped around the bottom sides of 150 the mold to remove air bubbles. The molds were then filled to the fill line and tamped again 151 about half to three-quarters depth from the fill line to prevent air bubbles. The top of the mold 152 was then tapped around the sides to release air bubbles. 153 After filling the molds, the fibers were embedded using a 3D printed mold cap to center 154 the fiber during curing. Half of the mold cap was attached using tape to the top of the mold. The 155 fiber was inserted through the center of the mold cap to the 10 mm mark followed by the 156 placement of the second half of the cap. The samples were demolded after 24 hours and cured 157 for 7 or 28 days in a 70˚F and 100% humidity curing chamber before single fiber pullout testing. 158 2.4. Biomineral coating characterization 159 2.4.1. Mineral texture and elemental composition 160 Samples of biomineralized fibers were imaged before and after SFPO testing using field 161 emission scanning electron microscopy (FESEM, Zeiss Supra 55VP, 1 kV, working distance 162 4.7-6.6 mm). These samples were first sputter-coated with gold to improve conductivity. 163 The elemental composition of the biomineral coating was determined for additional 164 biomineralized samples using energy dispersive x-ray spectroscopy (SEM-EDS) analysis 165 (FESEM, Zeiss Supra 55VP, Oxford detector, 15 kV, working distance 8.5 mm). Samples 166 studied with SEM-EDS were first coated with carbon. 167 2.4.2. Mineral identification 168 X-ray powder diffraction (Bruker D8 Advance Powder X-ray Diffractometer) was used to 169 characterize the crystalline structure of the CaCO3 biomineral precipitated on the fiber surface. 170 The biomineral was scraped off the fiber surface 2 days after deposition and ground to a powder 171 with mortar and pestle. MDI Jade was used to identify the diffractogram peaks. 172 2.4.3. Contact angle measurement 173 Video contact angle (VCA) measurements were acquired using a VCA 2500XE Video 174 Contact Angle System. DI water droplets of size 4.0 ± 0.5 μl were placed on the untreated 175 plastic fiber surface. The mean VCA of each plastic is reported from five measurements per 176 fiber. Contact angles less than 90˚ were considered hydrophilic while angles greater than 90˚ 177 were considered hydrophobic. 178 2.5. Single fiber pullout tests 179 2.5.1. Instrumentation 180 Single-fiber pullout (SFPO) tests were performed using an Instron 5543 with a 1kN load 181 cell (Figure 1). Aluminum base plates were milled to 150.0x76.2x19.05 mm. Samples were 182 centered on the plate and adhered with Crystalbond™ 509-1 adhesive. The base plate was 183 heated on a hot plate at 200˚C to melt the adhesive. The samples were cooled at room 184 temperature for a minimum 45-60 min before testing. 185 186 Figure 1: SFPO testing arrangement. (1) Fiber, (2) Pneumatic grips, (3) Crystalbond 187 adhesive, (4) base plate, (5) OPC cement mortar specimen. 188 2.5.2. Single-fiber pullout testing and analysis 189 The minimum free length of the fiber was 4.5 mm. The tensile rate was 1 mm/min until 190 the fiber was completely pulled out or snapped [30,34,40]. The pullout curves (load vs. 191 displacement) and fiber pullout properties were analyzed using MATLAB. 192 Pullout curves generated from SFPO tests were used to determine the interfacial bond 193 strength (𝜏𝜏𝑎𝑎), frictional bond strength (𝜏𝜏𝑏𝑏), chemical bond energy (𝐺𝐺𝑑𝑑), and energy absorption 194 (Figure 2). Values for 𝜏𝜏𝑎𝑎 and 𝜏𝜏𝑏𝑏 were calculated based on the peak load (Pa, Eq. 1) and the 195 load at which fiber pullout begins (Pb, Eq. 2) and where 𝑙𝑙 is the fiber embedded length, 𝑑𝑑 is the 196 fiber diameter, and 𝐸𝐸 is the fiber modulus [35,40,47–49]. 𝐺𝐺𝑑𝑑 was calculated using the load drop 197 from Pa to Pb, signifying the broken chemical bond between the fiber and cement matrix (Eq. 3) 198 [35,48,49]. The energy absorbed (work) during SFPO tests was assessed from the area under 199 the fiber pullout curve. 200 201 𝜏𝜏𝑎𝑎 = 𝑃𝑃𝑎𝑎/𝜋𝜋𝑑𝑑𝑙𝑙 (𝐸𝐸𝐸𝐸. 1) 202 𝜏𝜏𝑏𝑏 = 𝑃𝑃𝑏𝑏/𝜋𝜋𝑑𝑑𝑙𝑙 (𝐸𝐸𝐸𝐸. 2) 203 𝐺𝐺 = 2(𝑃𝑃 − 𝑃𝑃 )2/ 𝜋𝜋2𝐸𝐸𝑑𝑑3𝑑𝑑 𝑎𝑎 𝑏𝑏 (𝐸𝐸𝐸𝐸. 3) 204 The two regions of interest from the fiber pullout curves are the debonding region and 205 fiber pullout region labeled as A and B respectively in Figure 2. In the debonding region, the 206 chemical and frictional bond breaks before the fiber begins to displace. The pullout region 207 begins when the load drop from Pa to Pb occurs. The load-displacement behavior during fiber 208 pullout can be described as constant slip, slip softening, or slip hardening (Figure 2) [49]. 209 210 211 Figure 2: A standard pullout curve generated from single fiber pullout tests showing the 212 debonding (A), fiber pullout (B) regions and the three common frictional behaviors: 213 constant slip, slip softening, and slip hardening. 214 2.6. Statistical analysis 215 One-way ANOVA tested the effect of plastic type on contact angle and mineral 216 deposition on fiber surfaces. Two-factor ANOVA tested the effects of plastic type, 217 biomineralization treatment, and the interaction of these factors on measures from fiber pullout 218 testing. Significance was defined a priori at p<0.05. In the case of main effects with more than 219 two levels or in the case of significant interactions, a Tukey test was performed to discern 220 simple effects. A Tukey test is a post-hoc procedure that allows for multiple pairwise 221 comparisons while maintaining the overall family-wise error at α = 0.05. ANOVA models 222 satisfied assumptions of residual normality and equal variance. The response was transformed, 223 if necessary, to satisfy these assumptions. All analyses were performed using Minitab (v.19). 224 3. Results 225 3.1. Fiber surface and biomineral coating characterization 226 The MICP treatment was successful in depositing biomineral on all plastic types (Table 227 2, Figure 3). The amount of mineral per fiber and the ratio of mineral weight per gram of plastic 228 did not significantly differ by plastic type. XRD diffractograms (Figure 4) demonstrate that the 229 coating consists of mainly calcite and small amounts of vaterite. FESEM images suggest that 230 the biomineral is deposited in patches on the surface of each plastic type. EDS mapping 231 confirms that these surface deposits are calcium-rich, consistent with CaCO3 (Figure 3F). 232 Video contact angle (VCA) measurements identified that untreated ABS and PVC were 233 hydrophilic as their contact angles were less than 90˚. PVC was not hydrophobic (VCA of 234 87.66˚) but was near the hydrophobic threshold of 90˚ while ABS was more hydrophilic (VCA 235 82.46) than PVC. LDPE, PP, and PS were all hydrophobic, with contact angles greater than 90˚ 236 (Table 2). These VCA measurements are in general agreement with commonly reported contact 237 angles [50–52]. However, due to the material being recycled and formed into fibers, there may 238 be geometry and surface roughness characteristics that result in varying contact angles from 239 those previously reported. 240 241 Figure 3: FESEM images of microbially-induced calcium carbonate precipitation coatings on (A) 242 PVC, (B) LDPE, (C), PP, (D), PS, and (E) ABS fibers at approximately 350x magnification. (F) 243 EDS mapping of the calcium carbonate biomineral coating for treated PVC. 244 245 Figure 4: XRD diffractograms of biomineral deposited on plastic types 3-7. Diffractograms 246 reveal that calcite (c) is the major mineral formed and that vaterite (v) is a minor phase. 247 Table 2: Mineral precipitation and surface properties of plastic fibers. Measurements are 248 reported as mean ± standard deviation. Plastic Type Mineral precipitated g CaCO3/g fiber Contact Angle of (g) per fiber untreated fiber (˚) 3 PVC 0.04 ± 0.01 0.24 ± 0.05 87.66 ± 1.86 4 LDPE 0.03 ± 0.01 0.28 ± 0.07 98.13 ± 2.14 5 PP 0.04 ± 0.01 0.34 ± 0.11 98.94 ± 1.36 6 PS 0.04 ± 0.01 0.29 ± 0.07 96.44 ± 2.38 7 ABS 0.04 ± 0.01 0.35 ± 0.10 82.46 ± 5.54 249 250 3.2. Plastic type, not MICP treatment, is the main influence of bond strength 251 3.2.1. Fiber pullout behavior 7 Day 28 Day PVC LDPE PP ABS 252 253 Figure 5: Single fiber pullout curves for PVC (A), LDPE (B), PP (C), and ABS (D). The shaded 254 region surrounding the bolded mean line is the standard deviation (SD) from each pullout test. 255 The pullout curves from the SFPO tests are shown in Figure 5. The pullout curves 256 demonstrate that, in general, plastic type and not MICP treatment determine fiber pullout 257 behavior. The dominant pullout behavior for all treated and non-treated plastic types was slip 258 softening, as evidenced by the continual decrease of the load in the debonding region. PS 259 snapped before fiber pullout began and no pullout curves could be generated. The max loads 260 during single fiber pullout tests are given in Table 3. 261 262 263 Table 3: Max load (N) experienced during single fiber pullout testing at 7d and 28d timepoints. 264 All data reported as mean ± standard deviation. 7d 28d Plastic Type Untreated Treated Untreated Treated #3 PVC 36.17 ± 3.85 29.23 ± 1.56 36.28 ± 6.52 37.48 ± 5.27 #4 LDPE 12.41 ± 1.17 11.93 ± 1.32 11.84 ± 0.96 9.85 ± 1.92 #5 PP 27.06 ± 2.20 26.11 ± 3.20 27.08 ± 1.13 26.76 ± 1.52 #6 PS 45.65 ± 2.44 44.02 ± 2.35 46.96 ± 1.09 43.96 ± 2.62 #7 ABS 75.07 ± 12.82 73.78 ± 3.26 65.66 ± 17.62 69.68 ± 9.93 265 266 3.2.2. 7-day SFPO results 267 From two-factor ANOVA, there was a significant interaction between plastic type and 268 biomineral treatment on the interfacial bond strength (𝜏𝜏𝑎𝑎) and chemical bond energy (𝐺𝐺𝑑𝑑) 269 (p<0.05 for both). Post-hoc Tukey comparisons revealed that 𝜏𝜏𝑎𝑎 and 𝐺𝐺𝑑𝑑 were higher for 270 untreated PVC compared with treated PVC. For all other plastics, untreated and treated fibers 271 did not differ for either 𝜏𝜏𝑎𝑎 nor 𝐺𝐺𝑑𝑑. However, these measures showed differences by plastic type 272 (Figure 6). ABS had much higher interfacial bond strength and chemical bond energy than for 273 other plastics (Figure 6C). Grouping information from Tukey tests is shown in Table S.3. 274 Plastic type significantly affected frictional bond strength (𝜏𝜏𝑏𝑏) and work to pullout. 275 Biomineral treatment and the interaction between plastic type and biomineral treatment were not 276 significant. Post-hoc comparisons showed that the order from highest to lowest values for 𝜏𝜏𝑏𝑏 277 was ABS, PVC, PP, and LDPE, respectively (Figure 6B). ABS had the largest work to pullout, 278 followed by PVC and PP sharing the same mean, and LDPE had the lowest work to pullout 279 (Figure 6D). 280 281 Figure 6: (A) Interfacial bond strength, (B) frictional bond strength, (C) chemical bond energy, 282 and (D) work to pullout for single fiber pullout testing at 7 days of curing. Error bars indicate one 283 standard deviation. UT = untreated, T = MICP treated. n=5 for LDPE, PP, ABS, PVC (UT). n=3 284 for PVC (T). 285 3.2.3. 28-day SFPO results 286 For all plastic types, MICP treatment significantly lowered the mean values of 𝜏𝜏𝑎𝑎 and 𝜏𝜏𝑏𝑏 287 at 28 days (Figure 7A and 7B). Post-hoc comparisons of plastic type showed that at 28 days, 288 ABS had the highest mean values for both 𝜏𝜏𝑎𝑎 and 𝜏𝜏𝑏𝑏 followed by PVC, PP, and LDPE 289 respectively (Table S.4). 290 Plastic type significantly affected 𝐺𝐺𝑑𝑑 and work to pullout. MICP treatment did not 291 significantly affect these bonding characteristics. Tukey testing shows that ABS had the largest 292 𝐺𝐺𝑑𝑑, followed by PP and LDPE with similar means to each other, and, finally by PVC with the 293 lowest value (Figure 7C). Tukey tests showed that ABS and PVC shared the highest mean 294 work to pullout. Work to pullout was lower for PP than ABS, but PP and PVC were not 295 significantly different. LDPE had the lowest work to pullout (Figure 7D, Table S.4). 296 297 Figure 7: (A) Interfacial bond strength, (B) frictional bond strength, (C) chemical bond energy, 298 and (D) work to pullout for single fiber pullout testing at 28 days of curing. Error bars indicate 299 one standard deviation. UT = untreated, T = MICP treated. n=5 for each plastic type. 300 3.2.4. Post SFPO Test Surface 301 FESEM imaging was performed after SFPO testing for MICP treated and untreated 302 plastic fibers (Figure 8). From these images, no evidence of surface abrasions or peeling of 303 plastic surface were found for any plastic type. Post imaging revealed that nearly all the 304 biomineral had been removed from the fiber. Structures that appeared to be hydrated cement 305 and biomineral were occasionally seen on the fiber surfaces (Figure S.2). 306 307 Figure 8: Post-pullout FESEM images of A-D untreated and E-H treated PVC, LDPE, PP, and 308 ABS embedded sections, respectively. 309 4. Discussion 310 The purpose of this research was to determine the bonding characteristics between low- 311 value plastics and the cement mortar interface. It also served to test the hypothesis that MICP 312 treatment would increase the bond strength between PVC and cement mortar. While PVC, 313 LDPE, PS, and ABS are common low-value plastics that may be attractive for use in 314 cementitious materials, their bonding properties to the cement matrix are not well-understood. 315 Furthermore, while reports have shown that coating PP with CaCO3 via MICP [34] or other 316 methods [35] increased the interfacial bond strength with cement mortar, it is not known whether 317 MICP treatment improves the bond strength for other low-value plastics. In addition, the 318 feasibility of biomineralization on PVC, LDPE, PS, and ABS was largely unknow and therefore 319 investigated in this study. This work aimed to address these gaps by determining the interfacial 320 bond strength (𝜏𝜏𝑎𝑎), frictional bond strength (𝜏𝜏𝑏𝑏), chemical bond energy (𝐺𝐺𝑑𝑑), and work to pullout 321 for types 3-7 plastics with and without MICP treatment. 322 Differences in frictional strength and chemical bond energy contributed to the overall 323 variation in bond strengths between plastic types. ABS had the strongest values for all 324 measures, including 𝜏𝜏𝑎𝑎, 𝜏𝜏𝑏𝑏, 𝐺𝐺𝑑𝑑, and work to pullout. PVC, PP, and LDPE had progressively 325 lower 𝜏𝜏𝑎𝑎, 𝜏𝜏𝑏𝑏, and work to pullout. 𝐺𝐺𝑑𝑑 followed a different pattern. PVC had the lowest value, 326 followed by similar LDPE and PP, and finally ABS with the highest 𝐺𝐺𝑑𝑑. The determinants of bond 327 strength between the plastic fibers and the cement matrix may include fiber tensile strength, 328 roughness, and surface energy [23,39,49]. It was found that the variation in 𝜏𝜏𝑎𝑎 between fiber 329 types did not correspond with variation in tensile modulus (Table 1). Specifically, PVC and ABS 330 had the highest tensile moduli but had opposite bonding characteristics. For example, PVC had 331 an approximately 50% decrease in 𝜏𝜏𝑎𝑎 compared to ABS at both 7d and 28d time points. Fiber 332 roughness, as estimated from FESEM images, also does not seem to drive the results. PP 333 fibers appear to have the highest roughness but have midrange bond strengths compared with 334 the other plastics investigated (Figure 8). The water contact angle, which is related to the 335 surface energy, had good correspondence with chemical bond energy characteristics. ABS had 336 the strongest 𝐺𝐺𝑑𝑑 and was most hydrophilic. The other plastics either demonstrated 337 hydrophobicity (LDPE, PP, PS) or weak hydrophilicity (PVC) measured by their contact angles 338 with water (Table 2). The PS fibers broke before single fiber pullout testing was complete 339 (tensile stress was within 98% of the PS ultimate tensile strength, Table S.2), hence PS is not 340 included in the discussion of fiber surface characteristics or interfacial bonding parameters. 341 ABS had much stronger bond strengths with cement mortar, driven by higher 𝐺𝐺𝑑𝑑 and 𝜏𝜏𝑏𝑏 342 compared with PVC, LDPE, and PP. These data are in good correspondence with the 343 differences in compressive strength for PRM containing 5 wt% untreated plastic fibers reported 344 in prior work by Kane and coauthors [16]. In a prior study conducted by the authors, it was found 345 that 5 wt% ABS reinforced mortar without MICP treatment had higher compressive strength 346 than PRMs including untreated LDPE, PVC, PS, or PP fibers [16]. Others also report high 347 strengths of cementitious composites that utilize ABS. For instance, mortar prepared with a 5% 348 replacement of sand by ABS had higher compressive strength at 28 days than control mortar 349 [53]. Together, these results suggest that ABS may be a better choice for engineering higher 350 strength PRCs than other low-value recyclable plastics 351 Contrary to the initial hypothesis, the MICP biomineral treatment used in this work did 352 not improve bond strengths. In one case (PVC at the 7d time point), MICP treatment reduced 353 bond strengths and chemical bond energy. For all other plastics at both time points, MICP 354 treatment did not affect measures of the interfacial bond. These findings are in contrast with 355 other reports where the interfacial bonding properties of PP were improved with MICP [34] or 356 abiotic nano-CaCO3 treatments [35]. However, it is important to note that the measured bond 357 strength parameters for PP are in good correspondence with a previous study that used similar 358 embedment lengths and pullout rates without any treatments [40]. The differences in results 359 between the present study and these prior investigations may indicate that the method of 360 biomineral coating influences how it affects the bond strength. Hao et. al. [34] reported that a 361 0.094 CaCO3 g/g fiber coating improved interfacial bonding for PP and cement matrix more than 362 for either 0.026 CaCO3 g/g fiber or 0.374 CaCO3 g/g fiber coatings. In the present study, the 363 ratio of CaCO3 g/g fiber was well above 0.094 for all plastic types (Table 2). The thick, brittle 364 coating (Figure 3) may dissociate from the fibers and therefore not contribute to bonding with 365 the cement matrix. Adhesives may also improve the bonding of CaCO3 to plastic. A paraffin wax 366 coating used to adhere the abiotic nano-CaCO3 by Feng and coworkers resulted in improved 367 bond strength of PP to cement mortar [35]. Therefore, in some contexts, CaCO3 coatings 368 deposited by MICP or other methods, may have the potential to improve plastic bonding 369 strength to cement. 370 While MICP did not improve bonding parameters in this study, it was observed in the 371 author’s prior investigation that the same MICP treatment improved PRM composite strength for 372 5 wt% PVC and for a mixture of types 3-7 plastics [16]. These data indicate that the biomineral 373 likely influences other factors which lead to the increase in mechanical performance of PRM but 374 not the bond strength. MICP treatment may improve cement hydration around the interfacial 375 transition zone between treated fiber and mortar matrix or affect composite porosity. The 376 influence of MICP treatment on these other factors would benefit from additional investigation. 377 This study had several limitations. 3D printer filament was utilized because the uniform 378 filament size simplified SFPO testing and allowed comparisons between plastic types. These 379 filament dimensions are not ideal for PRM reinforcements. The sample size for PVC 7 day 380 treated samples was reduced to n=3 from n=5 because of a load frame error. Finally, 381 determining the impact of MICP treatment and plastic type on PRM hydration, porosity, and 382 durability were outside of the scope of the present study. 383 5. Conclusions 384 This study compared interfacial bond strength characteristics from single fiber pullout 385 testing for MICP treated and untreated plastic types 3-7 embedded in OPC mortar. Plastic type 386 had a large influence on measures of bond strength. ABS had superior interfacial bond strength 387 over PP, PVC, and LDPE plastics. The variation in bond strengths between plastic types more 388 closely corresponded with the surface energies of the fibers as opposed to surface roughness 389 or fiber tensile strength. MICP treatment did not significantly influence most interfacial bond 390 strengths, frictional bond strengths, chemical bond energies, or work to pullout measures at 391 either 7d or 28d of curing. In some cases, as for PVC at 7d of curing, MICP significantly lowered 392 measures of bond strength. The reason the MICP treatment did not improve the bond strength 393 in this work, is likely attributed to the thick and inconsistent coverage of biomineral over the fiber 394 surface. The results of this work demonstrate that the beneficial influence of MICP on PRM 395 compressive strength is not simply determined by an increase in bond strength. Furthermore, 396 these results demonstrate that plastic reinforcements can have quite different bonding strengths 397 with cement, which may be useful in the design of PRM and PRC. In particular, the high bond 398 strengths and chemical bond energies of ABS make this plastic an attractive candidate for PRM 399 and PRC applications. 400 Acknowledgments 401 The authors would like to thank the Montana Nanotechnology Facility, Montana State University 402 Undergraduate Scholars Program, and the McNair Scholars Program for funding M.E. This work 403 was performed in part at the Montana Nanotechnology Facility, a member of the National 404 Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science 405 Foundation (Grant# ECCS-2025391). S.K.’s contribution was funded by the Environmental 406 Research and Education Foundation Ph.D. scholarship. This material is based upon work 407 supported by the National Science Foundation, under grant CMMI 2036867. Any opinions, 408 findings, and conclusions or recommendations expressed in this material are those of the 409 authors and do not necessarily reflect the views of the National Science Foundation. We also 410 thank Dr. Stephen Sofie, Dr. Kirsten Matteson, and Dr. Michael Berry for access to equipment 411 as well as advice. Thank you to Dr. Sara Maccagnano-Zachar for assistance with XRD and 412 FESEM analysis and interpretation, and Jorge Osio-Norgaard and Dr. Roberta Amendola for 413 their technical advice on this work. 414 Declaration of competing interest 415 The authors declare no competing interests that could influence the work reported in this 416 publication. 417 Author Contributions 418 Conceptualization, M.E., A.P., C.R., C.H.; data curation, M.E., S.K.; formal analysis, M.E.; 419 funding acquisition, M.E., A.P., C.R., C.H.; investigation, M.E.; methodology M.E., S.K., C.H.; 420 writing—original draft, M.E, C.H.; writing—review and editing, M.E., S.K., A.P., C.H. and C.R. All 421 authors have read and agreed to the published version of the manuscript 422 6.0 References 423 [1] A. Naqi, J.G. Jang, Recent progress in green cement technology utilizing low-carbon 424 emission fuels and raw materials: A review, Sustainability (Switzerland). 11 (2019) 537. 425 https://doi.org/10.3390/su11020537. 426 [2] R.M. Andrew, Global CO 2 emissions from cement production, Earth System Science 427 Data. 10 (2018) 195–217. https://doi.org/10.5194/essd-10-195-2018. 428 [3] N. Makul, Modern sustainable cement and concrete composites: Review of current 429 status, challenges and guidelines, Sustainable Materials and Technologies. 25 (2020). 430 https://doi.org/10.1016/j.susmat.2020.e00155. 431 [4] R. Geyer, J.R. Jambeck, K.L. Law, Production, use, and fate of all plastics ever made, 432 Science Advances. 3 (2017). https://doi.org/10.1126/SCIADV.1700782. 433 [5] R. Geyer, Production, use, and fate of synthetic polymers, in: Plastic Waste and 434 Recycling, 2020: pp. 13–32. https://doi.org/10.1016/b978-0-12-817880-5.00002-5. 435 [6] B.S. Al-Tulaian, M.J. Al-Shannag, A.R. Al-Hozaimy, Recycled plastic waste fibers for 436 reinforcing Portland cement mortar, Construction and Building Materials. 127 (2016) 102– 437 110. https://doi.org/10.1016/j.conbuildmat.2016.09.131. 438 [7] N. Pešić, S. Živanović, R. Garcia, P. Papastergiou, Mechanical properties of concrete 439 reinforced with recycled HDPE plastic fibres, Construction and Building Materials. 115 440 (2016) 362–370. https://doi.org/10.1016/j.conbuildmat.2016.04.050. 441 [8] S. Gupta, H.W. Kua, S.Y. Tan Cynthia, Use of biochar-coated polypropylene fibers for 442 carbon sequestration and physical improvement of mortar, Cement and Concrete 443 Composites. 83 (2017) 171–187. https://doi.org/10.1016/J.CEMCONCOMP.2017.07.012. 444 [9] N. Saikia, J. De Brito, Use of plastic waste as aggregate in cement mortar and concrete 445 preparation: A review, Construction and Building Materials. 34 (2012) 385–401. 446 https://doi.org/10.1016/j.conbuildmat.2012.02.066. 447 [10] N. Saikia, J. de Brito, Mechanical properties and abrasion behaviour of concrete 448 containing shredded PET bottle waste as a partial substitution of natural aggregate, 449 Construction and Building Materials. 52 (2014) 236–244. 450 https://doi.org/10.1016/j.conbuildmat.2013.11.049. 451 [11] O.Y. Marzouk, R.M. Dheilly, M. Queneudec, Valorization of post-consumer waste plastic 452 in cementitious concrete composites, Waste Management. 27 (2007) 310–318. 453 https://doi.org/10.1016/j.wasman.2006.03.012. 454 [12] N. Haghighatnejad, S.Y. Mousavi, S.J. Khaleghi, A. Tabarsa, S. Yousefi, Properties of 455 recycled PVC aggregate concrete under different curing conditions, Construction and 456 Building Materials. 126 (2016) 943–950. 457 https://doi.org/10.1016/j.conbuildmat.2016.09.047. 458 [13] S.C. Kou, G. Lee, C.S. Poon, W.L. Lai, Properties of lightweight aggregate concrete 459 prepared with PVC granules derived from scraped PVC pipes, Waste Management. 29 460 (2009) 621–628. https://doi.org/10.1016/j.wasman.2008.06.014. 461 [14] M.J. Islam, M.S. Meherier, A.K.M.R. Islam, Effects of waste PET as coarse aggregate on 462 the fresh and harden properties of concrete, Construction and Building Materials. 125 463 (2016) 946–951. https://doi.org/10.1016/j.conbuildmat.2016.08.128. 464 [15] R. Wang, C. Meyer, Performance of cement mortar made with recycled high impact 465 polystyrene, Cement and Concrete Composites. 34 (2012) 975–981. 466 https://doi.org/10.1016/j.cemconcomp.2012.06.014. 467 [16] S. Kane, A. Thane, M. Espinal, K. Lunday, H. Armağan, A. Phillips, C. Heveran, C. Ryan, 468 Biomineralization of Plastic Waste to Improve the Strength of Plastic-Reinforced Cement 469 Mortar, Materials. 14 (2021) 1949. https://doi.org/10.3390/ma14081949. 470 [17] R. Sharma, P.P. Bansal, Use of different forms of waste plastic in concrete - A review, 471 Journal of Cleaner Production. 112 (2016) 473–482. 472 https://doi.org/10.1016/j.jclepro.2015.08.042. 473 [18] A.J. Babafemi, B. Šavija, S.C. Paul, V. Anggraini, Engineering properties of concrete with 474 waste recycled plastic: A review, Sustainability (Switzerland). 10 (2018). 475 https://doi.org/10.3390/su10113875. 476 [19] A.A. Ramezanianpour, M. Esmaeili, S.A. Ghahari, M.H. Najafi, Laboratory study on the 477 effect of polypropylene fiber on durability, and physical and mechanical characteristic of 478 concrete for application in sleepers, Construction and Building Materials. 44 (2013) 411– 479 418. https://doi.org/10.1016/j.conbuildmat.2013.02.076. 480 [20] N.L. Lovata, M.F. Fahmy, Interfacial bond study of a chemically treated polypropylene 481 fibre-reinforced concrete, Construction and Building Materials. 1 (1987) 83–87. 482 https://doi.org/10.1016/0950-0618(87)90004-3. 483 [21] A. Peled, H. Guttman, A. Bentur, Treatments of polypropylene fibres to optimize their 484 reinforcing efficiency in cement composites, Cement and Concrete Composites. 14 485 (1992) 277–285. https://doi.org/10.1016/0958-9465(92)90026-R. 486 [22] A.M. López-Buendía, M.D. Romero-Sánchez, V. Climent, C. Guillem, Surface treated 487 polypropylene (PP) fibres for reinforced concrete, Cement and Concrete Research. 54 488 (2013) 29–35. https://doi.org/10.1016/j.cemconres.2013.08.004. 489 [23] L. Akand, M. Yang, X. Wang, Effectiveness of chemical treatment on polypropylene fibers 490 as reinforcement in pervious concrete, Construction and Building Materials. 163 (2018) 491 32–39. https://doi.org/10.1016/j.conbuildmat.2017.12.068. 492 [24] S. Singh, A. Shukla, R. Brown, Pullout behavior of polypropylene fibers from cementitious 493 matrix, Cement and Concrete Research. 34 (2004) 1919–1925. 494 https://doi.org/10.1016/j.cemconres.2004.02.014. 495 [25] C. Zhang, V.S. Gopalaratnam, H.K. Yasuda, Plasma Treatment of Polymeric Fibers for 496 Improved Performance in Cement Matrices, Journal of Applied Polymer Science. 76 497 (2000) 1985–1996. https://doi.org/10.1002/(SICI)1097-4628(20000628)76:14<1985::AID- 498 APP1>3.0.CO;2-G. 499 [26] V.C. Li, H.C. Wu, Y.W. Chan, Effect of plasma treatment of polyethylene fibers on 500 interface and cementitious composite properties, Journal of the American Ceramic 501 Society. 79 (1996) 700–704. https://doi.org/10.1111/j.1151-2916.1996.tb07932.x. 502 [27] H. Wu, V.C. Li, Basic Interfacial Characteristic of Polyethylene Fiber/Cement Composites 503 and its Modification by Plasma, Proc., 5th International Symposium on Brittle Matrix 504 Composites. (BMC-5). (1997) 14–23. http://hdl.handle.net/2027.42/84756. 505 [28] B. Felekoglu, K. Tosun, B. Baradan, A comparative study on the flexural performance of 506 plasma treated polypropylene fiber reinforced cementitious composites, Journal of 507 Materials Processing Technology. 209 (2009) 5133–5144. 508 https://doi.org/10.1016/j.jmatprotec.2009.02.015. 509 [29] R. Hlůžek, J. Trejbal, V. Nežerka, P. Demo, Z. Prošek, P. Tesárek, Improvement of 510 bonding between synthetic fibers and a cementitious matrix using recycled concrete 511 powder and plasma treatment: from a single fiber to FRC, European Journal of 512 Environmental and Civil Engineering. (2020). 513 https://doi.org/10.1080/19648189.2020.1824821. 514 [30] P. di Maida, E. Radi, C. Sciancalepore, F. Bondioli, Pullout behavior of polypropylene 515 macro-synthetic fibers treated with nano-silica, Construction and Building Materials. 82 516 (2015) 39–44. https://doi.org/10.1016/J.CONBUILDMAT.2015.02.047. 517 [31] C. Signorini, A. Sola, B. Malchiodi, A. Nobili, A. Gatto, Failure mechanism of silica coated 518 polypropylene fibres for Fibre Reinforced Concrete (FRC), Construction and Building 519 Materials. 236 (2019). https://doi.org/10.1016/j.conbuildmat.2019.117549. 520 [32] F.U.A. Shaikh, Y. Shafaei, P.K. Sarker, Effect of nano and micro-silica on bond behaviour 521 of steel and polypropylene fibres in high volume fly ash mortar, Construction and Building 522 Materials. 115 (n.d.) 690–698. https://doi.org/10.1016/j.conbuildmat.2016.04.090. 523 [33] W. Zhang, X. Zou, F. Wei, H. Wang, G. Zhang, Y. Huang, Y. Zhang, Grafting SiO2 524 nanoparticles on polyvinyl alcohol fibers to enhance the interfacial bonding strength with 525 cement, Composites Part B: Engineering. 162 (2019) 500–507. 526 https://doi.org/10.1016/j.compositesb.2019.01.034. 527 [34] Y. Hao, L. Cheng, H. Hao, M.A. Shahin, Enhancing fiber/matrix bonding in polypropylene 528 fiber reinforced cementitious composites by microbially induced calcite precipitation pre- 529 treatment, Cement and Concrete Composites. 88 (2018) 1–7. 530 https://doi.org/10.1016/j.cemconcomp.2018.01.001. 531 [35] J. Feng, F. Yang, S. Qian, Improving the bond between polypropylene fiber and cement 532 matrix by nano calcium carbonate modification, Construction and Building Materials. 269 533 (2020) 121249. https://doi.org/10.1016/j.conbuildmat.2020.121249. 534 [36] W. de Muynck, N. de Belie, W. Verstraete, Microbial carbonate precipitation in 535 construction materials: A review, Ecological Engineering. 36 (2010) 118–136. 536 https://doi.org/10.1016/j.ecoleng.2009.02.006. 537 [37] A.J. Phillips, R. Gerlach, E. Lauchnor, A.C. Mitchell, A.B. Cunningham, L. Spangler, 538 Engineered applications of ureolytic biomineralization: A review, Biofouling. 29 (2013) 539 715–733. https://doi.org/10.1080/08927014.2013.796550. 540 [38] E. Wölfel, C. Scheffler, I. Curosu, V. Mechtcherine, Single fibre pull-out tests of 541 polypropylene and glass fibres in cement-based matrices at high loading rates, ECCM 542 2018 - 18th European Conference on Composite Materials. (2020) 24–28. 543 [39] E. Wölfel, H. Brünig, I. Curosu, V. Mechtcherine, C. Scheffler, Dynamic single-fiber pull- 544 out of polypropylene fibers produced with different mechanical and surface properties for 545 concrete reinforcement, Materials. 14 (2021) 1–20. https://doi.org/10.3390/MA14040722. 546 [40] D.L. Naik, A. Sharma, R.R. Chada, R. Kiran, T. Sirotiak, Modified pullout test for indirect 547 characterization of natural fiber and cementitious matrix interface properties, Construction 548 and Building Materials. 208 (2019) 381–393. 549 https://doi.org/10.1016/j.conbuildmat.2019.03.021. 550 [41] H.R. Pakravan, M. Jamshidi, M. Latifi, M.M. Chehimi, Polymeric fibre adhesion to the 551 cementitious matrix related to the fibres type, water to cement ratio and curing time, 552 International Journal of Adhesion and Adhesives. 35 (2012) 102–107. 553 https://doi.org/10.1016/j.ijadhadh.2012.02.006. 554 [42] Z. Lin, V.C. Li, Crack bridging in fiber reinforced cementitious composites with slip- 555 hardening interfaces, Journal of the Mechanics and Physics of Solids. 45 (1997) 763– 556 787. https://doi.org/10.1016/S0022-5096(96)00095-6. 557 [43] Y. Wang, V.C. Li, S. Backer, Modelling of fibre pull-out from a cement matrix, 558 International Journal of Cement Composites and Lightweight Concrete. 10 (1988) 143– 559 149. https://doi.org/10.1016/0262-5075(88)90002-4. 560 [44] A. Bhutta, M. Farooq, C. Zanotti, N. Banthia, Pull-out behavior of different fibers in 561 geopolymer mortars: Effects of alkaline solution concentration and curing, Materials and 562 Structures/Materiaux et Constructions. 50 (2017) 1–13. https://doi.org/10.1617/s11527- 563 016-0889-2. 564 [45] ASTM C305, Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and 565 Mortars of Plastic Consistency, ASTM Lnternational. (2011) 1–3. 566 https://doi.org/10.1520/C0305-14.2. 567 [46] ASTM, Standard Practice for Making and Curing Concrete Test Specimens in the 568 Laboratory, (2007) 1–8. https://doi.org/10.1520/C0192. 569 [47] T. Kanda, V.C. Li, Interface property and apparent strength of high-strength hydrophilic 570 fiber in cement matrix, Journal of Materials in Civil Engineering. 10 (1998) 5–13. 571 https://doi.org/10.1061/(ASCE)0899-1561(1998)10:1(5). 572 [48] Z. Lin, T. Kanda, V.C. Li, On interface property characterization and performance of fiber 573 reinforced cementitious composites, Journal of Concrete Science. 1 (1999) 173–184. 574 [49] C. Redon, V.C. Li, C. Wu, H. Hoshiro, T. Saito, A. Ogawa, Measuring and Modifying 575 Interface Properties of PVA Fibers in ECC Matrix, Journal of Materials in Civil 576 Engineering. 13 (2001) 399–406. https://doi.org/10.1061/(asce)0899- 577 1561(2001)13:6(399). 578 [50] D.K. Owens, R.C. Wendt, Estimation of the surface free energy of polymers, Journal of 579 Applied Polymer Science. 13 (1969) 1741–1747. 580 https://doi.org/10.1002/app.1969.070130815. 581 [51] L. Magallón Cacho, J.J. Pérez Bueno, Y. Meas Vong, G. Stremsdoerfer, F.J. Espinoza 582 Beltrán, J. Martínez Vega, Novel green process to modify ABS surface before its 583 metallization: optophysic treatment, Journal of Coatings Technology and Research. 12 584 (2015) 313–323. https://doi.org/10.1007/s11998-014-9632-5. 585 [52] P.F. Rios, H. Dodiuk, S. Kenig, S. McCarthy, A. Dotan, The effect of polymer surface on 586 the wetting and adhesion of liquid systems, Journal of Adhesion Science and 587 Technology. 21 (2007) 227–241. https://doi.org/10.1163/156856107780684567. 588 [53] G. Kaur, S. Pavia, Physical properties and microstructure of plastic aggregate mortars 589 made with acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), polyoxymethylene 590 (POM) and ABS/PC blend waste, Journal of Building Engineering. 31 (2020) 101341. 591 https://doi.org/10.1016/j.jobe.2020.101341. 592 593 594 595 Supplementary materials: Evaluation of the bonding properties between low-value plastic 596 fibers treated with microbially-induced calcium carbonate precipitation and cement mortar 597 Mineralization Plastic solution Fibers Stir Bar 598 599 Figure S.1: Diagram of the setup used for microbially-induced calcium carbonate 600 biomineralization of plastic fibers. 601 Table S.1: Weight of fibers (13 per group) before and after MICP treatment. Also shown the 602 biomineral weight accumulation per group. All data reported as mean ± standard deviation. Plastic Type Before After Biomineral Treatment (g) Treatment (g) accumulation (g) #3 PVC 2.11 ± 0.03 2.63 ± 0.11 0.52 ± 0.10 #4 LDPE 1.48 ± 0.01 1.89 ± 0.10 0.42 ± 0.10 #5 PP 1.39 ± 0.01 1.86 ± 0.15 0.47 ± 0.15 #6 PS 1.62 ± 0.01 2.09 ± 0.12 0.47 ± 0.12 #7 ABS 1.63 ± 0.01 2.19 ± 0.16 0.56 ± 0.17 603 604 Table S.2: Tensile strengths of plastic types and the percentage of tensile strength the max 605 load during single fiber pullout (SFPO) testing reached. Plastic Type Tensile Strength Max tensile stress experienced during (MPa) SFPO expressed as % of tensile strength #3 PVC 42.03 ± 1.90 33.21% #4 LDPE 9.58 ± 0.23 52.82% #5 PP 12.08 ± 0.53 91.49% #6 PS 19.02 ± 0.56 97.99% #7 ABS 9.58 ± 0.23 78.72% 606 607 Table S.3: Tukey post-hoc results and groupings at 7 days. Groupings of different letters signify 608 statistically different mean values. Post-hoc tests were only conducted for significant main 609 effects and interactions. 7-Day Interfacial Bond Strength Tukey Pairwise Comparisons: Plastic Type*MICP Treatment Interaction (MPa) Plastic N Mean Grouping Type ABS UT 5 1.34 A ABS T 5 1.26 A PVC UT 5 0.67 B PP T 5 0.50 C PVC T 3 0.49 C PP UT 5 0.47 C LDPE UT 5 0.24 D LDPE T 5 0.21 D Frictional Bond Strength Tukey Pairwise Comparisons: Plastic Type (MPa) ABS 10 1.01 A PVC 8 0.52 B PP 10 0.40 C LDPE 10 0.18 D Chemical Bond Energy Tukey Pairwise Comparisons: Plastic Type*MICP Treatment Interaction Response (J/m2) ABS UT 5 11.70 A ABS T 5 10.21 A PP UT 5 3.04 A B PP T 5 2.64 A B LDPE UT 5 1.36 B C LDPE T 5 0.89 B C PVC UT 5 0.39 C PVC T 3 0.03 D Work to Pullout Tukey Pairwise Comparisons: Plastic Type Responce (N-mm) ABS 10 279.11 A PVC 8 142.22 B PP 10 139.74 B LDPE 10 69.59 C 610 611 Table S.4: Tukey post-hoc results and groupings at 28 days. Groupings of different letters 612 signify statistically different mean values. Post-hoc tests were only conducted for significant 613 main effects and interactions. 28-Day Interfacial Bond Strength Tukey Pairwise Comparisons: Plastic Type Response (MPa) Plastic N Mean Grouping Type ABS 10 1.17 A PVC 10 0.62 B PP 10 0.46 C LDPE 10 0.19 D Interfacial Bond Strength Tukey Pairwise Comparisons: Treatment (MPa) Untreated 20 0.54 A Treated 20 0.47 B Frictional Bond Strength Tukey Pairwise Comparisons: Plastic type (MPa) ABS 10 0.90 A PVC 10 0.58 B PP 10 0.39 C LDPE 10 0.15 D Frictional Bond Strength Tukey Pairwise Comparisons: Treatment (MPa) Untreated 20 0.46 A Treated 20 0.39 B Chemical Bond Energy Tukey Pairwise Comparisons: Plastic Type (J/m2) ABS 10 8.73 A PP 10 1.95 B LDPE 10 1.01 B PVC 10 0.07 C Work to Pullout Tukey Pairwise Comparisons: Plastic Type (N-mm) ABS 10 252.48 A PVC 10 191.54 A B PP 10 156.42 B LDPE 10 56.79 C 614 615 Table S.5: Interfacial Bond strength (MPa) at 7d and 28d timepoints. All data reported as mean 616 ± standard deviation. 7d 28d Plastic Type Untreated Treated Untreated Treated #3 PVC 0.67 ± 0.04 0.50 ± 0.04 0.62 ± 0.11 0.62 ± 0.09 #4 LDPE 0.24 ± 0.03 0.21 ± 0.02 0.23 ± 0.01 0.17 ± 0.04 #5 PP 0.47 ± 0.04 0.50 ± 0.09 0.49 ± 0.03 0.44 ± 0.04 #7 ABS 1.36 ± 0.24 1.27 ± 0.14 1.24 ± 0.31 1.15 ± 0.15 617 618 Table S.6: Frictional bond strength (MPa) at 7d and 28d timepoints. All data reported as mean ± 619 standard deviation. 7d 28d Plastic Type Untreated Treated Untreated Treated #3 PVC 0.58 ± 0.07 0.48 ± 0.03 0.58 ± 0.11 0.59 ± 0.09 #4 LDPE 0.19 ± 0.03 0.18 ± 0.02 0.19 ± 0.01 0.13 ± 0.05 #5 PP 0.39 ± 0.04 0.41 ± 0.09 0.41 ± 0.02 0.38 ± 0.03 #7 ABS 1.05 ± 0.23 0.98 ± 0.05 1.00 ± 0.30 0.86 ± 0.14 620 621 Figure S.7: Chemical bond energy (J/m2) at 7d and 28d timepoints. All data reported as mean ± 622 standard deviation. 7d 28d Plastic Type Untreated Treated Untreated Treated #3 PVC 1.02 ± 1.19 0.03 ± 0.02 0.16 ± 0.16 0.12 ± 0.13 #4 LDPE 1.42 ± 0.42 0.96 ± 0.39 1.18 ± 0.57 1.22 ± 0.96 #5 PP 3.15 ± 0.91 2.71 ± 0.63 2.55 ± 1.43 1.98 ± 1.17 #7 ABS 12.20 ± 3.72 11.25 ± 5.45 7.24 ± 5.04 13.17 ± 4.86 623 624 Table S.8: Work to pullout (N-mm) at 7d and 28d timepoints. All data reported as mean ± 625 standard deviation. 7d 28d Plastic Type Untreated Treated Untreated Treated #3 PVC 134.86 ± 48.11 159.42 ± 26.75 174.23 ± 60.06 227.86 ± 61.96 #4 LDPE 67.73 ± 15.22 77.74 ± 27.60 66.41 ± 7.08 59.74 ± 32.40 #5 PP 149.52 ± 22.41 133.67 ± 23.15 147.62 ± 16.49 167.21 ± 15.84 #7 ABS 329.73 ± 134.83 255.80 ± 66.59 257.71 ± 101.93 281.70 ± 114.59 626 627 628 Figure S.2: Field Emission Scanning Electron Microscope images of the embedded sections 629 from polyvinyl chloride (A), linear low-density polyethylene (B), polypropylene (C), and 630 acrylonitrile butadiene styrene (D) microbially-induced calcium carbonate precipitation treated 631 fibers after single fiber pullout tests. Inserts show biomineral or cement hydration products 632 (portlandite and C-S-H gel) on the fiber surface. 633 634