Journal of Materials in Civil Engineering

In this paper, the coupled effects of sulfate (chemical factor) and curing temperature (thermal factor) on the strength development of cemented paste backfill (slag-CPB) that contains ground granulated blast furnace slag (slag) as a mineral admixture is studied. Almost 200 slag-CPB samples, cured at temperatures of 2, 20, 35, and 50°C at 28, 90, and 150 days with sulfate concentrations of zero ppm, 5,000 ppm, 15,000 ppm, and 25,000 ppm are tested for uniaxial compressive strength (UCS). The results show that the effect of sulfate on the strength of slag-CPB is significantly dependent on the curing temperature, initial sulfate content, and curing time. The coupled effects of sulfate and temperature can lead to an increase or decrease of the slag-CPB strength and significantly influence the type and amount of minerals formed within the cemented matrix of slag-CPBs. The strength-increasing factors are (1) refinement of the pore structure of slag-CPBs due to the precipitation of ettringite within the empty pores of the cemented matrix; (2) faster cement hydration rate and pozzolanic reaction with higher curing temperatures; and (3) activation of the slag reaction by sulfate ions. The identified strength-decreasing factors include (1) sulfate absorption by calcium silicate hydrate (C-S-H) that could lead to the formation of weaker C-S-H gel; (2) increase of ettringite dissolution as the curing temperature increases that results in the coarsening of the pore structure; (3) inhibition of cement hydration by sulfate; and (4) formation of hydration rims around the slag grains at high temperatures. There is competition between the strength-decreasing and increasing factors. The dominant influencing factors depend on the curing temperature, curing time, and initial sulfate content. A comparison of the performance of slag-CPBs and portland cement CPBs shows that a partial replacement of ordinary portland cement with slag improves the resistance of the studied cemented paste backfill at advanced ages and curing temperatures of 2°C and 20°C, while negatively affecting resistance for curing temperatures that are $\ge 35°\mathrm{C}$. This study has demonstrated that the coupled effects of sulfate and temperature on the strength of cemented paste backfill are an important factor that should be considered in the designing of cost-effective, safe, and durable cemented paste backfill structures.

Concrete is a globally accepted construction material in all types of civil engineering structures. The increase in construction has brought heavy demand for ingredients of concrete such as cement and sand, and these materials are becoming costly and scarce. The cost of cement is also steadily increasing. With ever-increasing environmental problems because of industrial waste products comes a great need to use these products in an appropriate manner to reduce health and environmental problems. Rice husk ash (RHA) and quarry dust (QD) are two such waste materials, the use of which in the production of concrete may prove advantageous in an agriculture-driven economy like the one in India, where rice is a major crop and QD is an abundantly available industrial waste product. This investigation attempts to use RHA and QD as partial replacements for cement and sand, respectively, in developing self-compacting mortar (SCM) mixes. The replacement percentage of cement by RHA varies in the range of 5–20%. On the basis of earlier results, an optimum percentage level of 40% sand replacement by QD is adopted. The compressive strengths of a control SCM mix (without RHA and QD) and compressive strengths of SCM mixes (with RHA and QD) are obtained experimentally at different ages of curing and are compared to assess the viability of adding RHA and QD in SCM mixes.

The capital city of India, Delhi, lies in the Indo-Gangetic alluvial trough. The soils of the Delhi region are known as “Delhi silt” because of the dominance of silt and, by and large, are nonplastic. The strength properties of Delhi silt, which contains either 60% or 20% sand, are experimentally evaluated with samples prepared using a slurry deposition technique in the laboratory and a stress-path triaxial system. Stress-strain-volume change and pore pressure behavior of these specimens under conventional triaxial compression (CTC) and the reduced triaxial extension (RTE) test for four values of confining pressures were measured, and strength properties are reported. These strength parameters as well as stress-strain volume change/pore pressure response were also compared with the results reported by other researchers; the observed behavior of Delhi silt is in good agreement with that of other silts reported in the literature. The study corroborated that the nature of Delhi silt is transitional, that is, it can be described by neither a sand nor a clay type of framework. All aspects of the mechanical behavior captured in this study (e.g., stress-strain volumetric response, pore pressure, and shear strength) were found to be affected by the amount of fines present in the sand and the loading conditions.

A cold in-place recycling (CIR) layer is typically overlaid by hot-mix asphalt (HMA) to protect it from water ingress and traffic load. Most public agencies have different curing requirements that specify the number of curing days or the maximum moisture content for the CIR layer before placing the HMA overlay. However, these criteria are not well-founded on sound engineering principles and are often challenged by contractors, especially in inclement weather conditions. This study was performed to explore technically sound ways to identify the minimum in-place CIR properties necessary to permit the placement of an HMA overlay. The primary objective of this research was to determine how curing time and moisture content affect the development of indirect tensile strength, dynamic modulus, and flow number of CIR mixtures composed of foamed asphalt (CIR-foam) or emulsified asphalt (CIR-emulsion). On the basis of the limited test results, the indirect tensile strength of CIR specimens did not increase during an early stage of curing but increased during a later stage of curing, usually when the moisture content was less than 1.5%. Given the same curing time, CIR-foam specimens exhibited more tensile strength and less moisture content than CIR-emulsion specimens. Both dynamic modulus and flow numbers increased as the curing time increased and the moisture content decreased. Given the same moisture content, CIR-foam specimens exhibited higher dynamic modulus and larger flow numbers than CIR-emulsion specimens.

Hot-mix asphalt is a mixture of aggregates and asphalt binder in appropriate ratios to produce a high-performing material for asphalt pavements. The aggregate structure, which depends on the gradation, is an important factor in determining the volumetric properties of HMA. The design process to determine the optimal aggregate blend is currently iterative and engineers rely almost exclusively on experience. This approach is time consuming and often results in suboptimal HMA mixtures. This study presents linear programming optimization models and attendant solution procedures that minimize HMA aggregate cost and produce high-quality HMA. The models are validated with real-life examples, and results indicate that the models are useful to replicate HMA mixes during field modifications, reduce the aggregate cost in a mixture, and manage stockpile inventory. The application of optimization models will increase the application of the Bailey method in the United States.

Two methods for strengthening two-way reinforced concrete floor slabs subjected to out-of-plane bending loads are compared through experiments on seven test specimens and subsequent analyses. The seven test specimens were two unstrengthened regular reinforced concrete slabs (control), two slabs strengthened using glass-fiber-reinforced polymer (GFRP) sheets, and three slabs strengthened with an innovative method of applying a layer of fiber-reinforced cement (FRC) in varying thicknesses to the tension face of the slab. All specimens were $1.5\mathrm{m}\times 1.5\mathrm{m}$ ($5\mathrm{ft}\times 5\mathrm{ft}$) and were designed to resist bending in both directions. The advantages and disadvantages of the two strengthening methods are discussed in terms of structural considerations, e.g., increase in load carrying capacity and ductility, and construction considerations, e.g., economy and ease of application. Experimental results show a significant increase in the ultimate load capacity of all five strengthened slabs over the two control slabs. The FRC-strengthened slabs exhibit superior ductility and larger measured displacements than the GFRP-strengthened slab. The two methods are comparable in terms of ease of application but FRC is more cost-effective. Theoretical values, which are calculated using existing analytical methods, such as strain compatibility, yield-line analysis, and, as appropriate, flexural shear stress analysis, are generally in good agreement with experimental data. Furthermore, by modifying similar analytical methods for fiber-reinforced polymers (FRPs) found in the literature an analytical method is derived for FRC. The methodologies utilized here provide a means for analysis and design of such rehabilitation schemes. As a result of this study, it is concluded that FRC has great potential as a strengthening method, and future work is recommended to further optimize the proposed strengthening technique.

Traditionally, the extent of sulfate attack is qualified through visual rating or quantified by the percent expansion of slender bars completely submerged in sulfate solution. There are currently no standardized test methods that take into account the change in engineering properties because of deleterious mechanisms. Moreover, the exposure regime used to evaluate sulfate attack, complete immersion, is not typically representative of that encountered in the field. For these reasons, the objective of the research presented herein is to quantify the degree of sodium sulfate attack through the degradation of mechanical properties, specifically the compressive and splitting tensile load capacities of standard cylindrical specimens. A novel exposure regime is utilized wherein the specimens are only partially submerged in 5% sodium sulfate solution, creating an evaporation front similar to that of field exposure. It was found that the portion submerged in sulfate solution, although visually pristine, was the weaker portion of the cylinder for both mechanical tests, even though the other half showed extensive signs of surface disintegration caused by salt crystallization.

The objective of this study is to investigate the sensitivity of aggregate size within sand mastic by modeling the microstructure of an asphalt mixture. The sensitivity of the maximum aggregate size on the sand mastic phase is investigated through discrete-element simulations. A three-dimensional (3D) discrete-element model of asphalt mixture was prepared from X-ray computed tomography (X-ray CT) images. In the discrete-element model, an asphalt mixture is divided into aggregate, sand mastic, and air void phases. In this study, the sand mastic is defined as fines and fine aggregates mixed with asphalt binder. Three different nominal maximum aggregate sizes (NMASs) of sand mastic, namely, 1.18 mm, 0.6 mm, and 0.3 mm, were used in the 3D model to investigate the best gradation of sand mastic. The dynamic moduli of three different NMASs of sand mastic were measured for use in the 3D discrete-element modeling simulation. Laboratory-measured dynamic moduli of asphalt mixtures were compared with prediction results. The sand mastics with NMASs of 1.18 mm and 0.6 mm could be used to predict the asphalt mixture modulus across a range of temperatures and loading frequencies with good accuracy. The sand mastic with a NMAS of 0.3 mm overpredicted at high and low temperatures. The overprediction resulted from the difficulty of proper visualization of the smaller aggregate size in the model.

This paper investigates the use of the strut-and-tie model to calculate the capacity of longitudinally reinforced cement-stabilized rammed earth deep beams with no shear reinforcement. Beams with a span-to-depth ratio ($L/D$) less than 10 and reinforced only by longitudinal steel bars represent the majority of lintels used to span openings such as windows, doors, and garage entrances. The strut-and-tie model is used in this work to analyze these structural members. This paper studies the failure modes and ultimate loads of 13 beams subject to two-point loading at quarter spans, with span-to-depth ratios ranging from 1.7 to 10. The results indicate that the strength of beams with span-to-depth ratios up to 10 can be predicted by the proposed method when the failure is dictated by the yielding of the tie. The compression capacity of the strut is more difficult to calculate because of the discrepancy between the compressive strength of small rammed samples and the real strength of rammed earth of large structural members. For this reason, the calculation of the capacity of beams failing for compression of the strut needs a more conservative approach and further research.

This paper describes the role of lightweight synthetic particles (LSP) on the restrained shrinkage cracking behavior of mortar in sealed conditions. The free shrinkage, elastic modulus, split-tensile strength, and restrained shrinkage behavior of mortar were investigated with respect to the inclusion of low volumes of LSP. Although the use of the LSP increases free shrinkage, decreases tensile strength, decreases elastic modulus, and increases stress relaxation, these particles can be beneficial in reducing the stress that develops when shrinkage is restrained. This can result in a delay or possible prevention of restrained shrinkage cracking.

A computational approach is offered for smoothing asphalt concrete complex modulus test results in a way that forces compliance with linear viscoelastic theory and thermorheological simplicity. Essentially, it is based on presupposing the shape of the relaxation spectrum with calculations carried out in the wicket domain. The suggested scheme calls for the determination of six free parameters—three of which are associated with the mechanical (viscoelastic) response, while the remaining three are related to the time-temperature shifting properties and include (as unknown) the reference temperature level. In the evaluation process, it is shown how the first three parameters can be obtained directly from the measurements and separately from the other three, while the determination of the latter set follows as a second independent step. This decoupled process simplifies the analysis and includes additional advantages. In this paper, the smoothing approach is described and discussed, and its appropriateness and relevancy for asphalt concrete materials is demonstrated using a sample data set.

The corrosion resistance of glass-fiber-reinforced polymer (GFRP) rebars makes them a promising substitute for conventional steel reinforcing rebars in continuously reinforced concrete pavements (CRCPs). Studies are conducted concerning the effect of using GFRP rebars as reinforcement in CRCP on the concrete stress development, which is directly related to the concrete crack formation that is inevitable in CRCP. In this study, an analytical model of a freely supported reinforced concrete slab is first developed to simulate the shrinkage and thermal stress distributions in concrete owing to the restraint provided by GFRP rebars in comparison with the stresses induced by steel rebars. The results show that the stress level in concrete is reduced with GFRP rebars owing to a low Young’s modulus of GFRP. In addition, the analytical model is utilized to estimate the concrete strain variation in the reinforced concrete slabs resulting from changes in the concrete volume, and the results are compared with the experimental observation. Finite-element (FE) analyses were also conducted to calculate the stress distribution and crack width of a GFRP-reinforced CRCP section subjected to both the concrete shrinkage and thermal change. By using the FE method, the crack spacing and crack width of a CRCP reinforced with GFRP rebars were predicted and compared with those of a steel-reinforced CRCP. The result shows that the crack spacing and the crack width of the GFRP-CRCP are larger than those of the steel-CRCP.

The rheological and chemical properties of hydrated lime-polyphosphoric acid (PPA)–modified asphalt binders before and after laboratory oxidative aging were investigated through dynamic shear rheometer (DSR) and nuclear magnetic resonance (NMR) tests. Ten percent by weight of hydrated lime was mixed with 1.5% by weight of PPA-modified asphalt binders. The neat asphalts and multimodified asphalts were subjected to the pressure aging vessel test at a pavement service temperature of 60°C for different durations. The rheological properties of unaged and aged modified asphalts were measured with a DSR at various temperatures. NMR was used to investigate whether hydrated lime reacts with PPA. The rheological results indicate that the addition of hydrated lime to PPA-modified asphalt binders cancels the stiffening effect of PPA. In other words, the addition of PPA to asphalt increases the high-temperature performance grade (PG). The addition of hydrated lime to PPA-modified asphalt removes the benefit of the high-temperature PG that PPA provided. Furthermore, hydrated lime reduces the rate of oxidative age hardening. The interaction between hydrated lime, PPA, and asphalt binders is asphalt-type-dependent. The interaction between sol-type asphalts and hydrated lime and PPA is different from that of gel-type asphalts.

The mechanical properties of wrought iron from multiple elements of six late 19th-century truss bridges is evaluated by a program of destructive and nondestructive testing, including hardness testing and tension tests to evaluate the yield stress ($F_y$), tensile strength ($F_u$), and ductility of the material. The yield stress and tensile strengths are found to be in accordance with those published in period reports and in other modern evaluations of the mechanical properties of wrought iron. The main findings of this work come from a statistical analysis of the test results and are (1) that hardness is a poor predictor of yield stress and tensile strength but has some predictive ability for ductility; (2) that there is a statistically significant difference in the distribution of yield stress and tensile strength between material samples from different bridges and, in some cases, between material samples from different members within a single bridge; and (3) that a size effect is present in the material that results in lower yield stress and tensile strength for larger members. These results provide guidance to engineers in the evaluation of historic iron trusses for rehabilitation and suggest that although nondestructive hardness testing is of limited value, a limited program of destructive testing can provide an adequate characterization of the mechanical properties throughout the bridge.

The hydration chemistry of sewage sludge ashes (SSAs) used as cement components is examined using X-ray diffraction, thermal analysis, and isothermal conduction calorimetry. The presence of SSA leads to the formation of significant quantities of ${\mathrm{A}{\mathrm{l}}_2\mathrm{O}}_3$-${\mathrm{F}{\mathrm{e}}_2\mathrm{O}}_3$-mono (AFm) phases. Large quantities of amorphous hydration products are also formed. An additional series of small-scale experiments is used to show that it is highly probable that amorphous or poorly crystalline hydroxyapatite (${\mathrm{Ca}}_5({\mathrm{PO}}_4{)}_3\mathrm{OH}$) is generated in addition to calcium silicate hydrate gel. Thus, the reactions of SSA in combination with portland cement cannot be viewed simply as comparable to the pozzolanic or latent hydraulic reactions of other by-product materials used in similar ways.

Bituminous crack sealants are commonly used for pavement maintenance. While cracks in pavement are inevitable, sealing the cracks helps maintain the integrity of the pavement by preventing water and debris from entering the structure. Sealing cracks increases pavement service life up to 5 years, and this can lead to significant cost savings for the U.S. highway system. Crack sealing is a cost-effective maintenance approach, provided that the right sealant is selected and properly installed. However, sealant selection is difficult because of the lack of a rheology-based standard test that correlates with field performance. To address this drawback, performance-based guidelines for the selection of hot-poured crack sealants have been developed by a research team, including the writers. To complement these guidelines, this paper describes a recently developed adhesion test procedure that predicts interface bonding based on a fundamental property of the interface, interfacial fracture energy (IFE). This recently developed pressurized blister test is a fracture test. The principle of the test is to break the interface bonding by pressurizing the interface between the adhesive and adherend. The amount of pressure and the deformation of the adhesive before and during the debonding period are used to calculate the IFE. The test variation is acceptable because its average coefficient of variation is 8.7%. This paper describes the test apparatus and procedure and discusses the adhesion of several hot-poured bituminous sealants to aluminum, limestone, quartzite, and granite.

The voids in mineral aggregate (VMA) design parameter is one of the most important in the current Superpave mix design procedure that links hot-mix-asphalt (HMA) mix properties to field performance. The success of achieving the appropriate VMA at an early stage of the mix-design process not only significantly impacts the design time and effort but also can produce an economical and reasonable design with good field performance. Although several current mix and gradation design methods have provided some guidance on adjusting gradation to achieve target VMA, these approaches still have to rely on initial experimental results with some degree of trial and error, and provide no direct correlation between aggregate gradation and VMA. This paper presents an analysis of aggregate packing and discrete-element modeling (DEM) simulation to link the aggregate gradation property to the VMA of HMA. A new definition is proposed for characterizing traditional dense-graded aggregate gradations into three types: coarse-graded, medium-graded, and fine-graded. A gradation weighing factor, $f_v$, defined as the percentage of voids change by volume caused by unit additional aggregate, is developed to theoretically evaluate the packing of an aggregate structure. A method of VMA estimation based on the generated $f_v$ values is thus provided. Eleven mix designs from different states are used for verifying the accuracy of the prediction. Most predictions are within 1% difference of the design VMA. Using one nominal maximum aggregate size (NMAS) of 12.5 mm as an example, this study provided a promising method for a fast and accurate VMA estimation. It can be used directly in the HMA mix design to reduce the design time and effort, and contribute to the estimation of the HMA mixture performance at an early stage of the design period.

The effect of steel fibers in improving the bond performance of hooked-bar anchorages installed in high-strength concrete (HSC) beam-column connections was evaluated by testing twelve beam-column type specimens. The specimen simulated the rigid connection of a vertical cantilever beam to a base column. The tensile beam reinforcement consisted of two bars anchored in the column outside the column reinforcement cage using hooked-bar anchorages. The variables used in the study were the beam bar size (16, 25, or 32 mm) and the volume fraction of steel fibers added and dispersed in the concrete mix (0, 0.5, 1.0, or 1.5%). Analysis of the test results revealed that steel fibers were effective in increasing the anchorage capacity and the ductility of the load-deflection history of specimens with steel fibers as compared with companion specimens identical in geometry and bar size but without steel fibers.

This study shows the results of a research project conducted to study the technical feasibility of the reconstruction of a real marine structure of natural rock. The experimental campaign enables the analysis of the behavior of stainless steel anchorages adhered with polymeric adhesives for strengthening the stone structure. To this end, mechanical tests were carried out to characterize the adhesive-steel-stone system and to verify the static effectiveness of anchorages, both in situations of nonimmersion and immersion in seawater. Tensile tests in anchorages under cyclic loading were performed in addition to other trials to estimate the bond stress under shear of epoxy polymer adhesive with the stone substrate and bending tests to evaluate the performance of stones reinforced with epoxy polymer mortar and stainless steel. The results obtained provide for an advance in the difficult field of the selection of materials potentially applied to the reinforcement of structures subjected to complex and varied mechanical actions, particularly in highly aggressive environments, such as seawater.

The present research aims to quantify the influence of the curing time period, amount of cement, porosity, and voids/cement ratio in the assessment of unconfined compressive strength ($q_u$) of artificially cemented sand. A program of unconfined compression tests considering distinct curing time periods ($t$), porosities ($\eta$), and cement contents ($C$) was carried out in the present study. It has been found that a power function adapts well unconfined compressive strength values with increasing cement content and with reducing porosity of the compacted mixture. As expected, the unconfined compressive strength of the cemented sand increases with an increasing curing time period. It was also shown that the voids/cement ratio ($\eta /C_v$) is a good parameter in the evaluation of the unconfined compressive strength of the cemented sand studied, for the whole range of cement and porosities studied, at each specific curing time period studied. Finally, a unique relationship can be achieved linking the unconfined compressive strength ($q_u$) with the voids/cement ratio ($\eta /C_v$) and the curing period ($t$).

High porosity with interconnected voids between aggregate particles is the primary characteristic of portland cement pervious concrete (PCPC), which, however, causes a significant decrease in its strength and abrasion resistance. In this study, latex and fiber were added to improve the abrasion resistance of PCPC mixtures. Laboratory tests were conducted to evaluate the performance of latex-modified pervious concrete with a particular focus on abrasion resistance. Test results show that adding latex desirably improved strength and abrasion resistance of PCPC, whereas fiber did not show a significant effect on the mechanical properties of PCPC. In addition, the asphalt pavement analyzer (APA) abrasion test was found to be feasible for evaluating the abrasion resistance of pervious concrete.

Owing to its importance in evaluating the fracture behavior of concrete, the crack extension resistance curve of concrete has been widely studied, both experimentally and theoretically. In this paper, a numerical approach is developed for the crack extension resistance curve of concrete by considering the variation of the fracture process zone (FPZ) length during the whole fracture process. In this approach, the FPZ length is determined by using the linear asymptotic superposition assumption. Dividing the whole fracture process into three different stages of the cohesive stress distribution within the FPZ, the crack extension resistance curve is formulated by superposition of the intrinsic fracture toughness of concrete and the fracture toughness caused by the cohesive stress within the FPZ. The developed numerical approach is applied to the tested and simulated standard three-point bending notched concrete beams. The effect of the variation of the FPZ length on the crack extension resistance curve is evaluated on the basis of the numerical results. The crack extension resistance first increases with an increase in ratio of the effective crack length to the beam depth and then reaches a plateau value when the FPZ is fully developed. When the effective crack length is normalized to the beam depth, the crack extension resistance is basically independent of the beam depth within the beam size range studied.

This paper presents the results of a laboratory experimental program to evaluate the potential of limestone dust (LSD) and coal fly ash (CFA) to stabilize some problem soils in southeastern Pennsylvania. Some of the geotechnical characteristics of the soils investigated include Atterberg limits, compaction, California bearing ratio (CBR), swell, and unconfined compressive strength (UCS). A one-way analysis of variance (ANOVA) test performed on the generated data confirmed that LSD and CFA contents significantly influenced the compaction and the strength characteristics of Philadelphia soils stabilized with these additives. Results of the study showed that the plasticity and swell of the soils were reduced by 40% and between 40 and 70%, respectively. The results further showed a marked increase in strength of the soils for CBR and UCS when stabilized with the additives.

This paper reports the recycling of bagasse ash (waste product of sugar industries) as a cement replacement in concrete, which provides a satisfactory solution to environmental concerns associated with waste management. The impact of bagasse ash content as a partial replacement of cement has been investigated on physical and mechanical properties of hardened concrete, including compressive strength, splitting tensile strength, chloride diffusion, and resistance to chloride ion penetration. The results indicate that bagasse ash is an effective mineral admixture and pozzolan with the optimal replacement ratio of 20% cement, which reduced the chloride diffusion by more than 50% without any adverse effects on other properties of the hardened concrete.

Experiments were conducted to investigate the odometric swell behavior of expansive soil specimens mixed independently with two different granular additives: silica sand and granulated tire rubber (GTR). All specimens were prepared with the same global water content. However, specimens that contained sand swelled less than did analogous specimens that contained GTR, regardless of the surcharge stress imposed before inundation. Phase relationship analyses based on “oversize correction” equations derived for mixtures with three solid phases indicate that the specimens possessed clay portions with different dry density and initial water content. Such differences are attributed mainly to the role of additive grain stiffness during specimen preparation. Results from complementary discrete element method simulations indicate that the stiffness of the additive grains may also play a role in mitigating the swell via contact force alterations upon swell.