•Well-graded samples (SW and SC-SW) performed better than the poorly-graded samples (SP).•At 300 psi or higher, fine aggregates can be replaced up to 20%.•Results indicate that fine aggregates can be ...successfully replaced by drill cuttings.
Drill cutting (DC) is a major waste produced during petroleum extraction, which could present a major source of contamination to soil and groundwater, if not disposed properly. The objective of this study aims to test the hypothesis that drill cuttings can be incorporated as an aggregate in the production of concrete, and is suitable for use in controlled, low-strength material (CLSM) for non-structural applications. To achieve this objective, the physical and consensus properties of drill cuttings were characterized. Concrete mixtures were designed for CLSM applications with and without drill cuttings sampled from two sources. Prepared concrete mixes were then evaluated in terms of strength for use in non-structural concrete applications. Results showed that well-graded drill cuttings performed better than poorly-graded samples. Furthermore, when compared to the control samples, no significant compressive strength reduction was observed for concrete mixes prepared with drilled cuttings at high strength targets (2800, 1200 and 300 psi). Yet, a significant reduction was observed at low strength targets (80 and 200 psi). This may be due that the higher content of cement in high strength concrete mixtures compensates for the lack of strength as a result of drill cuttings. At high strength targets, it is feasible to replace the fine aggregates up to 20% without reducing the target compressive strength significantly.
•Two full-scale jointless ECC-UTW sections (101.6-mm and 63.5-mm thick, respectively) were constructed and monitored.•Generally, mechanical properties of ECC manufactured on a large-scale ...underperformed those of ECC manufactured under laboratory conditions.•Seven months post-construction, the 63.5-mm thick ECC-UTW presented microcracks attributed to normal functioning of ECCs’ PSH mechanism. Yet, the 101.6-mm thick ECC-UTW exhibited macrocracks associated mainly with areas of heavy instrumentation and/or where fiber clumps occurred.•Due to potential jointless functionality and thickness reduction, ECC-UTWs may present a cost-effective alternative to conventional concrete UTWs.
The objective of this study was to evaluate the construction, material characterization, initial structural assessment, and cost of a novel jointless Engineered Cementitious Composite Ultra-Thin Whitetopping (ECC-UTW) overlay. After construction, early-age cracks (from less than 0.25 mm to up to 2.54 mm width) were observed in the 101.6-mm (4 in.) jointless ECC-UTW section; yet, the majority of the cracks coincided with areas where fiber clumps were observed during construction and places of heavy instrumentation. On the other hand, no cracks were observed in the 63.5-mm (2.5 in.) jointless ECC-UTW at early ages; yet, when winter arrived, micro-cracks (<0.25 mm in width) developed. These micro-cracks were attributed to the normal functioning of the ductile pseudo strain-hardening (PSH) mechanism of ECC materials. Falling Weight Deflectometer (FWD) evaluation conducted before and after the construction of the UTWs showed a significant reduction in pavement deflection after construction. This deflection reduction was much more substantial for thicker 101.6-mm UTWs; yet, no major difference in deflection reduction was found between the 101.6-mm ECC and the 101.6-mm regular concrete UTW sections. The 28-day compressive and flexural strength of ECC evaluated from field specimens underperformed that of previous studies by 9.6% and 14.8%, respectively; however, deflection capacity slightly outperformed that of previous studies by 4.1%. The flexural performance of the ECC material was vastly superior to that of regular concrete exceeding the flexural strength by 92%. All specimens evaluated in uniaxial tension exhibited a PSH behavior after first-cracking; however, the tensile strength and tensile ductility values obtained underperformed expected values for ECC M3-15% and exhibited substantial variability. Uniaxial tensile test results from field specimens were deemed unreliable. Cost analysis results showed that a cost reduction of 14.8% per lane kilometer is expected by implementing the proposed jointless ECC-UTW system compared to that of the regular jointed concrete UTW. The greatest construction cost savings for utilizing ECC originates from its potential jointless attribute and its reduced thickness.
The objective of this study was to evaluate the feasibility of developing practical and cost-effective ultra-high-performance engineered cementitious composites (UHP-ECCs) using natural river sand ...and no silica fume (SF). Fresh and hardened properties of composites utilizing river sand, with and without SF, and incorporating 1.5 and 2 vol% (volume percent) ultra-high-molecular-weight polyethylene fibers were evaluated. Furthermore, matrix and fiber/matrix interface properties were investigated. Experimental results showed that the inclusion of SF generally produced negative impacts in the mechanical strength (i.e., compressive, tensile, and flexural) and ductility of the composites, which was mainly attributed to a worsening fiber dispersion. This was supported by the loss in workability observed when increasing fiber content or implementing SF. Clear tendencies in the effect of fiber content on the mechanical strength of the composites were not observed. However, increment in fiber content decreased the tensile ductility of the materials, presumably because of poor fiber dispersion. All the mixtures evaluated exhibited pseudo strain-hardening (PSH) behavior and ECC-like ductility, which was supported by the PSH strength and energy indexes obtained, which exceeded the minimum recommended values for robust PSH behavior. Practical and cost-effective UHP-ECC materials (i.e., cementitious composites simultaneously exhibiting compressive strength >120 MPa and tensile strain capacity >2%) using natural river sand and no SF were successfully developed, which to the authors’ knowledge was achieved for the first time.
AbstractThe main objective of this study was to evaluate calcium nitrate tetrahydrate as a healing agent and its efficiency in concrete materials. This investigation focused on improving the ...mechanical properties of microcapsule-containing concrete by both altering the microencapsulation procedure and modifying the concrete mix design. Results showed that both the introduction of the newly developed microcapsules and a defoamer in the mix design were key in minimizing the air content of microcapsule-containing concrete, and thus resulted in improved mechanical properties comparable to the control groups. The differences in the virgin modulus of elasticity values between the control groups and the microcapsule-containing specimens were minimal. However, microcapsule-containing specimens at the lowest concentrations were significantly less affected by damage cycles than the control specimen groups. In addition, several microcapsule-containing specimens showed significant healing potential with respect to compressive strengths and modulus of elasticity after damage, surpassing the control specimens. Based on these results, the optimum microcapsule concentration lies between 0.25 and 0.50% by weight of cement for axial compressive loads.
Bacterial concrete has become one of the most promising self-healing alternatives owing to its capability to seal crack widths through microbial-induced calcite precipitation (MICP). In this study, ...two bacterial strains were embedded at varying dosages (by weight of cement) in concrete. Beam specimens were used to quantify the maximum crack-sealing efficiency, whereas cylinder samples were used to determine their effects on the intrinsic mechanical properties of concrete, as well as its stiffness recovery over time after inducing damage. The concrete specimens were cured in wet–dry cycles to enable healing. Results showed that the specimen groups with the highest calcium alginate concentrations (including the control specimens with embedded alginate beads but no bacteria) resulted in the greatest increase in stiffness recovery. Similarly, the beam samples containing alginate beads (also including the Control 3%C specimen group) had superior crack-healing efficiencies to the control samples without alginate beads (Control NC). This was attributed to the alginate beads acting as a reservoir that can further enhance the autogenous healing capability of concrete. Based on the results of this study, further research is recommended to explore factors that can maximize the self-healing mechanism of bacterial concrete through MICP and determine whether an alternative encapsulation mechanism, nutrient selection, curing regime, or bacterial strain is needed.
AbstractThe main objective of this study is to evaluate and optimize the crack healing efficiency of hydrogel-encapsulated bacteria in concrete applications. To achieve this objective, Bacillus ...pseudofirmus was evaluated as the bacteria strain, which was combined with three mineral precursors corresponding to magnesium acetate, calcium lactate, and sodium lactate at two concentrations (67.76 and 75 mM/L). For each combination, three sets of mortar cubes, along with three sets of mortar beams, were prepared. The mechanical properties of these specimens were characterized by compressive and flexural strength tests. Once the beams were cracked, they were subjected to 28 days of wet/dry cycles in which crack width was monitored. Once the wet/dry cycles were completed, the specimens were retested to determine the strength recovery. In the compressive strength and self-healing efficiency tests, mortar samples prepared with calcium lactate at a concentration of 75 mM/L along with bacteria and yeast extract showed the best performance. With respect to flexural strength recovery, no significant difference was noted among the specimens. Microscopic evaluation revealed a high concentration of calcium-rich crystals (i.e., calcium carbonate or calcium hydroxide crystals) indicative of bacterial activities. A scale-up concrete study was performed based on the best-performing mortar samples and then compared to plain concrete. Results from the concrete analysis indicated that the addition of calcium lactate improved concrete’s flexural strength. However, the plain concrete control specimen displayed superior healing efficiency after being subjected to wet/dry cycles.
AbstractThis paper presents an evaluation of dual self-healing mechanisms in concrete, with a focus on the application of microcapsules and shape memory alloy (SMA). To achieve this objective, the ...study evaluated the self-healing effectiveness of calcium nitrate microcapsules in concrete beams reinforced with steel and SMA. The undamaged stiffness, damaged stiffness, peak strengths, and deformations were measured and compared with postcuring time values. Further, crack monitoring coupled with an energy-dispersive X-ray (EDX) spectroscopy analysis was used to evaluate crack healing over time and to characterize the healing components in the cracked areas. Experimental results suggest that microcapsules caused a direct effect on decreasing the flexural strength of concrete beams, attributing the results to the presence of high air content when the microcapsules are used. Although microcapsules tended to lower the flexural strength of the beams, the stiffness recovery values were higher for those specimens prepared with microcapsules. An image analysis conducted after the water curing period revealed that specimens with microcapsules showed the best crack healing efficiency, regardless of the use of steel or SMA. In the use of heat activation, not only was crack healing efficiency observed with SMA, but also a noticeable difference was found in SMA samples, with or without microcapsules.
Ultrathin whitetopping (UTW) is a rehabilitation technique that consists of pouring a thin layer of concrete on top of distressed asphalt pavement. UTW has shown satisfactory performance in the ...field; however, due to the brittleness of concrete, early pavement failure has been reported. Engineered cementitious composites (ECC) have been considered for UTW applications due to its superior tensile ductility, flexural performance, and fatigue resistance in order to serve as an alternative to concrete. To investigate this application, an ECC-UTW was constructed at the Pavement Research Facility (PRF) in Port Allen, Louisiana. A critical factor that contributes to the performance of UTWs is the bond strength with the existing asphalt concrete (AC) layer. Therefore, prior to loading, a series of laboratory bond tests were conducted on drilled core specimens to characterize the strength of ECC/AC and concrete/AC interfaces. Two existing AC surface conditions were considered: milled and unmilled. ECC/AC and concrete/AC specimens were prepared and subjected to direct shear in accordance with AASHTO TP 114. Furthermore, the tensile bond strength was assessed through the pull-off test by ASTM C1583. Results showed that concrete had a superior bond strength with AC compared to ECC under the direct shear condition. In addition, the pull-off tests carried out in the UTW also indicated that concrete had a superior bond in tension with the AC substrate compared to ECC. Interfaces were analyzed by scanning electron microscopy–electron dispersive X-ray spectroscopy (SEM–EDS), and findings indicated a lack of hydration products at the ECC/AC interface.
This study investigates the mechanical and physical properties of engineered geopolymer composites (EGCs) consisting of metakaolin (MK) based geopolymer (GP) binder, microsilica sand (MS) or river ...sand (RS), and polyvinyl alcohol (PVA) fiber. Plain GP matrices and fiber-reinforced composites were studied. Aspects of the material composition evaluated here included binder composition, aggregate type, and fiber content. Compressive strength test results revealed that GP mortars presented greater compressive strength than pure GP binders. Moreover, the addition of PVA fibers produced an important increment in compressive strength while increases in fiber content generally enhanced compressive strength. MS composites tended to produce higher compressive strength than RS composites. While exhibiting low densities (i.e., 1.80–1.94 g/cm3), the composite materials evaluated exceeded the compressive strength of regular concrete (i.e., 30 MPa). Furthermore, the best performing composite presented a compressive strength of 57.5 MPa, thus falling in the category of high-strength concrete. The EGC-like tensile pseudo strain-hardening (PSH) behavior of MK-based GP composites was confirmed by a uniaxial tensile test with MS-composites exhibiting greater tensile strength and ductility compared with RS composites; yet, robust PSH behavior was not achieved mainly because of a lack of proper fiber dispersion. Scanning electron microscopy (SEM) revealed unreacted metakaolin particles in some areas within the geopolymer gel of both GP binders evaluated in this study, suggesting incomplete geopolymerization in the binder. Furthermore, energy dispersive X-ray spectroscopy (EDS) microchemical analysis of a geopolymer gel encountered close agreement between the target composition of the GP binders produced and the actual chemical composition encountered in the specimens evaluated.
The objective of this study was to investigate the effects of different mixing processes, particularly a two-stage mixing process, on fresh and hardened characteristics of pastes and concrete. ...Characteristics studied for pastes included rheological effects (i.e., yield stress, thixotropy, viscosity, and peak stress) and compressive strength for mixes prepared in a Hobart mixer and a high-shear mixer. Parameters measured for the concrete study included fresh concrete air and slump, compressive strength, and hardened concrete air void characteristics. The paste study results show that for increased mixing time, the compressive strength is not significantly influenced. The rheology results show that longer mixing times with a high-shear mixer lead to lower viscosity, thixotropy, and peak stress; this indicates better-mixed slurry when compared with a shorter mixing time and the Hobart mixer. The fresh concrete made with the two-stage mixing process shows reduction in air content, and the hardened concrete shows little change in compressive strength when compared with the concrete produced with the one-step mixing process. Rapid air void analysis results indicate that the two-stage mixing method may be beneficial for mixes containing portland cement as a sole binder in freeze-thaw durability.
