Journal of Materials in Civil Engineering

The study examined several formulations that may serve as a green substitute for traditional portland cement. The primary objective of the project was to produce a durable, low-energy cementitious material from flue gas desulfurization (FGD) gypsum that was converted to hemihydrate. The study also included spent ash from circulating fluidized bed combustion (CFBC), and Class F fly ash. Hemihydrate would give the by-product cement early strength development, and the spent-bed/ultrafine ash blend would provide the by-product cement with long-term strength (gaining slowly at first) and decrease solublity. A spent-bed/ultrafine ash ratio of $40/60$ produced the best compressive-strength results of the preliminary clinkerless cement blends produced in the study. The expansion of these clinkerless cements was caused by the formation of ettringite shown by X-ray diffraction (XRD). The system stopped expanding when calcium hydroxide was largely consumed. Substituting 50% of the clinkerless cement blends with hemihydrate increased short-term compressive strength 200% and reduced longer-term expansion up to 90%, enabling the production of low-energy 100% by-product cement.

In this study, a robust variant of genetic programming, namely gene expression programming (GEP) was utilized to build a prediction model for the strength of concrete under triaxial compression loading. The proposed model relates the concrete triaxial strength to mix design parameters. A comprehensive database used for building the model was established on the basis of the results of 330 tests on concrete specimens under triaxial compression. To verify the predictability of the GEP model, it was employed to estimate the concrete strength of the specimens that were not included in the modeling process. Further, the model was externally validated using several statistical criteria recommended by researchers. A sensitivity analysis was carried out to determine the contributions of the parameters affecting the concrete strength. The proposed model is effectively capable of evaluating the ultimate strength of concrete under triaxial compression loading. The derived model performs superior when compared with other empirical models found in the literature. The GEP-based design equation can readily be used for predesign purposes or may be used as a fast check on solutions developed by more in-depth deterministic analyses.

This paper presents findings from a recently completed research study at the University of Illinois aimed at investigating the effects of aggregate type and quality on mechanistic pavement response and rutting performance with implications to over 2.6 million km (1.6 million miles) of unsurfaced roads in the United States. Three aggregate types, crushed limestone, crushed dolomite, and uncrushed gravel, were tested in the laboratory for resilient modulus ($M_R$) and permanent deformation characteristics at different factorial combinations of selected aggregate physical properties. Aggregate properties studied included particle shape and surface texture, type and amount of fines, and moisture and density in relation to required compaction conditions. Stress-dependent material characterization models determined from the laboratory $M_R$ tests were used in a nonlinear axisymmetric finite-element analysis program to compute the vertical compressive stress on top of the subgrade as a critical pavement response. The adequacy of the aggregate layer to carry wheel loads and prevent subgrade rutting was evaluated using the concept of the subgrade stress ratio (SSR), defined as the ratio between the vertical stress on top of the subgrade and the subgrade unconfined compressive strength. The laboratory testing and modeling showed that the aggregate physical properties had significant influences on both the modulus and permanent deformation behavior of unbound aggregates. In addition to protecting the subgrade from rutting by means of placing stiff (high $M_R$) aggregate layers on top, a properly designed unsurfaced pavement system should also evaluate the susceptibility of the aggregate cover itself to excessive rutting, preferably through permanent deformation testing of the aggregates. The findings clearly highlighted the importance of considering both the load spreading and rut resistance aspects of the unbound aggregate layer in the design of unsurfaced pavements. The significance of different aggregate properties affecting modulus and permanent deformation model parameters was identified through statistical analyses of variance (ANOVA) conducted on the laboratory test results.

This paper presents an alternative criterion (simplified method) to determine the cohesion ($c$) and internal angle of friction ($\phi$) properties for two granular materials lightly stabilized with slag lime and general blend (GB) cement–fly ash using indirect diametral tensile (IDT) strength and unconfined compressive strength (UCS). The $c$ and $\phi$ values of the stabilized materials obtained on the basis of this criterion were related to the IDT strength and UCS. The results suggest that the $c$ and $\phi$ can be estimated using this criterion and the $c$ can be accurately related to either the IDT strength or UCS for lightly cementitiously stabilized granular materials. However, the IDT strength is a better characteristic than the UCS to estimate the $c$. To validate the criterion, the $c$ and $\phi$ obtained from the proposed criterion were input in the numerical analyses of IDT testing with Mohr-Coulomb failure criterion using FLAC2D finite difference software. The predicted tensile stress–horizontal diametrical deformation numerical results were compared with the corresponding experimental results. On the basis of this numerical analysis, the $c$ and $\phi$ parameters estimated from this method could predict the experimental results well in the elastic region but over-predicted the ultimate stress.

The mechanical deterioration of concrete exposed to freeze-thaw cycles is one of the most important durability problems under subzero temperature conditions. At present, studies on concrete behavior under freeze-thaw cycles primarily focus on the degradation of concrete properties, there are few reports on testing and modeling the stress-strain relationships of concrete undergoing repeated cycles of freeze-thaw. This paper investigated the stress-strain relationship of fly ash concrete under 0, 5, 15, 30, 50, 75, 100, and 125 freeze-thaw cycles by testing 24 prism specimens. The relative dynamic modulus, compressive strength, elastic modulus, and stress-strain relationship of specimens under freeze-thaw cycles were measured. In addition, a multiple sharp degradation point model for the degradation of mechanical properties of concrete was proposed. Finally, a damage constitutive model on the base of the damage mechanics and the multiple sharp degradation point model was presented. By comparing the results calculated by the damage constitutive model with the experimental data, the proposed model was proved to be effective for evaluating the stress-strain relationship of fly ash concrete under freeze-thaw cycles.

In this research, the performance of three rapid methods for evaluation of chloride resistance of concrete, including the rapid chloride penetration test (RCPT), rapid chloride migration test (RCMT), and electrical resistance test, are compared. Because the ability of the RCPT method to evaluate of concrete mixes containing supplementary cementitious materials has been questioned by some researchers, the mixes studied included the control mix and mixes containing 2.5, 5, 7.5, and 10% silica fume (SF); 7.5 and 15% fine fly ash (VFA); 15 and 30% fly ash (FA); 15 and 30% pumice (PU); and 15, 30, and 50% slag (SL). The results of all three methods show a considerable decrease in chloride permeability of mixes containing silica fume at the ages of 28 and 90 days and mixes containing other supplementary cementitious materials at 90 days. However, the RCPT test considerably overestimated the improvement compared to the other two methods, mainly as a result of the temperature rise effect in this test. Despite the simplicity and speed of the electrical resistance test, its results correlate well with those of the RCMT test.

A new technology of constructing ultra-thin antiseepage walls by polymer injection has been developing. The mechanism of polymer expanding and filling the slot formed by the direct pushing method is studied in this paper. The expansion-filling mechanism of the polymer in the preset slot in soil is simulated with the finite-volume method (FVM) and the volume-of-fluid (VOF) method. The construction technology of polymer injection is also investigated. The injecting effect has been verified through field experiment and the antiseepage effect of the formed wall has been theoretically analyzed by the finite-element method (FEM). The results show that the polymer-injection technology is suitable for forming a continuous anti-seepage wall in earth dams or dikes.

A novel manufacturing process for wood-polypropylene composite (WPC) panels reinforced with fiber-reinforced polymer (FRP) sheets was implemented using a double belt pressing technology. FRP sheets were placed on both sides of the WPC agglomerates during fabrication, which resulted in increased productivity and reduced thermal stresses compared with secondary bonding processes. Significant improvements in the mechanical properties of the FRP reinforced sheet panels were found during flexural and tensile tests on the coupon level. Even with addition of only one layer of FRP reinforcement on both sides of a WPC panel, the flexural modulus and strength increased by a factor of 2.6 and 3.8, respectively. Furthermore, the flexural and tensile properties of the WPC material considered in this study were found to be superior compared with the properties of an extruded WPC material. The changes in the flexural modulus of the FRP reinforced WPC panels with respect to the number of FRP layers were predicted using a model based on moment-curvature analysis.

This paper demonstrates the potential for using field-applied structural coatings to reinforce traditional framing members and standard building ties, thereby providing an improved and continuous foundation to roof load pathway. Tension tests were performed on light-frame rafter to top plate connections, some of which were reinforced with a hurricane tie, to establish how much of a difference a polyurea coating made as the joints between the stud and top plate, and top plate and rafter, were loaded to failure. The tests indicate that polyurea provides universal strengthening compared with hurricane ties with the added advantage that members and joints can be protected from a multitude of threats, including corrosion attributable to moisture, damage attributable to flood; and, with self-extinguishing properties fire. The addition of the coatings allowed both unreinforced and reinforced configurations to withstand higher loads (200–400% more). In general, the polyurea delayed the onset of failure and significantly strengthened every configuration by increasing the amount of work/energy required to pull it apart; in some cases, by almost 800%.

Fiber-reinforced self-consolidating concrete (FRSCC) has a tremendous potential to be used in construction industry because it combines the advantages of both self-consolidating concrete (SCC) and fiber-reinforced concrete (FRC). Nineteen concrete mixtures are developed by incorporating different dosages (up to 0.5% volume or $22\mathrm{kg}/{\mathrm{m}}^3$ of concrete) of polyvinyl alcohol (PVA) and metallic fibers and their combinations. The influences of fiber types, size, dosages, and fiber combinations (used in hybrid mixes) on fresh (slump flow, L-box passing ability, V-funnel flow time, and segregation index—a measure of workability) and rheological (viscosity and yield stress at various time intervals ranging from 10 to 70 min) properties are critically analyzed on the basis of experimental results. The workability/rheological properties of concrete mixtures are found to depend on types, dosages, geometry of fiber, and in cases of hybrid mixtures, interaction and synergic properties between different fiber types also play a critical role. The maximum dosage of PVA is limited to 0.125% compared with 0.3% of metallic fibers in developed FRSCC mixtures because of PVA’s higher workability reduction/viscosity increase capability. In addition, relationships among fresh/workability and rheological properties are also established.

An investigation was conducted into the beneficial utilization of captured ${\mathrm{CO}}_2$ for early-age curing of precast concrete products. The performance of the carbonation-cured concrete was compared to that of steam curing to investigate the possibility of replacing steam curing with carbonation. The early-age carbonation curing was performed for a short period after an initial curing in a controlled environment. The effect of the carbonation curing was studied in terms of carbon uptake, accelerated strength, and durability. It was found that the short-term carbonation promoted early strength development, while subsequent hydration was essential to obtain later age properties. Durability performance of the carbonation-cured concrete was compared with steamed and normally hydrated references. The carbonation-cured concrete exhibited more resistance to chloride permeability, ion migration, sulfate attack, and freeze-thaw damage. The improved durability by carbonation is attributed to the significantly reduced calcium hydroxide content at the carbonated concrete surface. Despite a reduced pH at the carbonated zone, the alkalinity at the core was maintained above the threshold value needed to prevent carbonation corrosion.

This paper deals with progressive substitution of hydrated lime by granulated blast furnace slag to produce new calcium silicate materials obtained by autoclaving, representing an alternative economic raw material. The slag grain-size grinding and the heat treatment in saturated vapor pressure autoclave conditions were investigated to study the compressive strength behavior of the new material. The results showed a decrease in compressive strength from the substitution. The microstructure analysis showed that reaction products consist mainly of 11 Å tobermorite and xonotlite. When increasing the autoclave temperature, it results in an increase in xonotlite relative to tobermorite. It is also observed that the amorphous composition of granulated blast furnace slag does not release new distinct phases of hydrates. The autoclaved products were characterized using X-ray diffraction (XRD) technique and scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDX).

Adequate damping capacity of concrete material is critical for concrete structures to resist impact loads. The effectiveness of styrene-butadiene latex as a polymer admixture for improving the vibration reduction capacity of concrete matrix is evaluated in this study by using a micromechanical-based numerical approach aided with laboratory experimental work for determining material parameters and validating a developed numerical model. By using the discrete element method (DEM), a user-defined three-dimensional (3D) model was developed to study the dynamic flexural responses of styrene-butadiene latex admixed concrete in the loss tangent, storage modulus, and loss modulus at three loading frequencies: 0.2, 1, and 5 Hz and a typical ambient temperature: 25°C. The 20% usage of styrene-butadiene latex, by weight of cement, was found to favorably enhance the storage and loss moduli and the loss tangent of concrete. Results from this combined numerical and experimental study can be expected to benefit the design of more resilient concrete materials and structures.

A multiscale model is established for effective diffusion coefficient of chloride ions in cement-based composite materials. The model takes into account the relationship between the diffusivity and microstructure of cement-based materials, where the microstructure includes the interfacial transition zone (ITZ) between the aggregate particles and the bulk cement pastes, and the microstructure of the bulk cement paste itself. In addition, the model also includes the parameters such as water-to-cement ratio, hydration degree of cement, the thickness of ITZ, the volume fraction, and gradation of aggregate. A model for predicting the porosity distribution in ITZ is proposed based on the cement-particle distribution and modified Powers model, and then effective chloride diffusivities of ITZ can be estimated. Thus, the effective diffusion coefficient is predicted by $n$-layered inclusion theory in which mortar and concrete is considered as four-phase materials consisting of matrix phase, aggregate, ITZ, and their homogenization phase at a mesoscopic level. To validate the proposed model, the diffusion coefficient of chloride ions by the steady-state migration test is measured on a series of mortar and concrete and compared with the calculated data. The results show that the model prediction agrees quite well with the available test results.

Clay roofing tiles fired at five different temperatures (900, 920, 960, 1,000, and 1,020°C) were subjected to the investigations of textural characteristics and frost resistance prediction. The closed container and hydraulic pressure mechanisms proved to be dominant at lower firing temperatures (900 and 920°C), whereas micro-ice-lens formation mechanism have significant role at higher temperatures (960 and 1,000°C). The highest resistance is noticed for the samples fired at 1,020°C where the frost action mechanisms are balanced because the porous structure that compensates the local stresses developed during freezing. The prediction of frost action durability of clay roofing tiles, the appearance of the first cracks, and the prediction of frost action mechanisms given by the statistical model, showed a high level of agreement. The statistical model contains capillary pores ($P_{0.1}$), and the ratio of frozen and unfrozen water ($I$) as significant parameters for describing susceptibility to closed container mechanism and micro-ice-lens formation mechanism, respectively.