Journal of Materials in Civil Engineering

In an effort to extend the reutilization of sewage sludge ash and improve the properties of sludge ash tiles, nano- ${\mathrm{SiO}}_2$ was applied as an additive to sludge ash tiles. Improvements in the tiles were evaluated by factors such as the amount of clay that was replaced by incinerated sewage sludge ash, the quantity of nano- ${\mathrm{SiO}}_2$ added, and the kiln temperatures. Furthermore, the effects of nano- ${\mathrm{SiO}}_2$ on the structure and mechanism of sludge ash tiles were studied from both microscopic and macroscopic views. Results indicate that the bending strength of sludge ash tiles increased with increased amounts of nano- ${\mathrm{SiO}}_2$ . However, due to brittle structures formed on the surfaces of tile bodies at temperature of $\mathrm{1,150}°\mathrm{C}$ or higher, reductions in bending strength were correlated with increasing amounts of nano- ${\mathrm{SiO}}_2$ added.

This paper assesses durability of a high-strength concrete with large volumes of supplementary cementitious materials modified by a polyethylhydrosiloxane-based admixture and a superplasticizer. The study introduces the concept of a modified multicomponent binder, comprised of portland cement, finely ground supplementary cementitious material (fly ash, ponded ash, or granulated blast furnace slag), and a highly reactive powder component (usually silica fume), modified by a superplasticizer. The research program included tests of water permeability, freezing and thawing resistance, and the investigation of the effect of the binder on the passivation of steel reinforcement. The observations indicated that the use of the superplasticizer and polyethylhydrosiloxane admixtures yields the required air content and air void spacing factor for the freezing and thawing resistance, and the passivation of steel reinforcement. The research confirmed that the polyethylhydrosiloxane admixture has a beneficial effect on the durability of concrete with large volumes of supplementary cementitious materials. The results have important implications for offshore structures, bridges, roadways, pavements, foundations, precast concrete, and other applications.

As part of a research program investigating the effects of supplementary cementing materials (SCMs) on the performance of concretes subjected to deicer salt scaling, a field trial was initiated in 1994. A series of six in-ground pavement slabs were cast with concretes containing various proportions of SCMs and exposed to a cyclic freeze/thaw environment, deicer salt application, and regular heavy truck loads for a period of $12\text{years}$ . The concretes consisted of a control mix with 100% portland cement, slag mixes containing 25, 35, and 50% blast furnace slag, a fly ash mix containing 15% Class C fly ash, and a ternary blend mix with 25% slag and 10% fly ash. Two sets of laboratory deicer salt scaling specimens were prepared concurrently with the in-ground slabs; one was immediately cured and tested in accordance with the applicable standard, whereas the second set was left on site and subjected to the same exposure conditions as the in-ground slabs for $4\text{months}$ (prior to freezing) before testing. Damage exhibited by the in-ground slabs and the $4\text{month}$ exposed scaling slabs was far less significant than that produced by the specimens subjected to standardized testing.

Past work has made little differentiation between the mechanical properties of pit and spun cast gray iron water pipes. Mechanical tests on coupons from spun and pit cast samples presented here show that spun cast gray iron has mechanical properties that fall between those of pit cast gray iron and ductile iron pipes, often with marked similarities to ductile iron. The properties determined from the mechanical tests were used to examine whether linear elastic analysis can be successfully used to approximate the mechanical behavior of a pipe loaded in bending. Linear elastic analysis was found to produce reasonable approximations to the behavior of undamaged pipes. The effect of corrosion pitting was included in the analysis by determining stress concentration factors for pits of varying depths at different stress levels. Multiplying the stress concentration factors by the results of the linear elastic analysis produced results with an error of no more than 6% from the values produced by a full cast iron plasticity analysis within the experimentally measured range of ultimate stresses.

Calcareous soils are used as graded base course materials in the Eastern Province of Saudi Arabia. The specimens tested in the laboratory are different from those in the field because of the removal of the oversize particles. The effects of maximum aggregate size on the load carrying capacity of calcareous fines (marl)-gravel mixture were studied. A large-size mold that can accommodate particles up to $50.8\mathrm{mm}$ was used to study the effect of oversize particles. Limestone aggregates (LSA) and steel slag aggregates (SSA) were used. The results indicate that the California bearing ratio (CBR) and the Clegg impact value (CIV) increase with the increase in the maximum aggregate size. The increase in the CBR values can reach 19% when the maximum aggregate size was increased from $19.05\text{to}50.8\mathrm{mm}$ . The CBR values for the calcareous fines-SSA mixtures were greater than those for the calcareous fines-LSA mixtures by up to 24%. The conventional CBR mold overestimates the CBR values by up to 43%. The results also clearly indicate the strong correlation between the CBR and the CIV results.

Significant recent advancements in cement-based, fiber-reinforced composite materials have stretched the bounds of concrete into the realm of ultrahigh-performance concrete (UHPC). The durability of a commercially available UHPC was independently evaluated through six standardized durability tests and the results are reported herein. Regardless of the curing treatment applied, this concrete exhibits significantly enhanced durability properties as compared to normal and high performance concretes. The concrete exhibited minimal damage after being subjected to two times the normal number of ASTM C 666 freeze–thaw cycles. It was innocuous to ASTM C 1260 ASR deterioration, to ASTM C 672 scaling deterioration, and to AASHTO T259 chloride penetration. The ASTM C 1202 Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration test result was negligible if any steam-based curing treatment was applied, and was very low otherwise. Steam-based curing treatments significantly enhanced the ASTM C 944 abrasion resistance. The curing treatment applied to this concrete can affect the durability properties, partly due to steam treatment increasing the degree of hydration of the concrete, improving its microstructure, and decreasing its permeability.

This paper presents the results of an experimental study to evaluate the damage and failure mode of hybrid-fiber engineered cementitious composite (ECC) panels caused by large projectiles or fragments. The aim is to quantify the extent to which hybrid-fiber ECC improves the resistance of blast panels against impact loading. Drop weight tests were conducted on full-scale hybrid-fiber ECC blast/shelter panels $(2\mathrm{m}\times 1\mathrm{m}\times 0.05–0.1\mathrm{m})$ to study their response and performance under impact loading. Conventional steel reinforced concrete (RC) and steel fiber-reinforced concrete (FRC) blast panels were also tested to identify the advantages of using ECC in this application. Both the drop weight projectile with a hemispherical head and the panel specimen were instrumented to facilitate evaluation of the global and local response. The impact resistance of blast panels of different materials is evaluated in terms of the extent of damage, energy absorption capacity and residual resistance against multiple impacts. The drop weight impact test results showed that the hybrid-fiber ECC panels exhibit lesser damage, significantly improved impact resistance against multiple impacts and improved ductility and energy absorption capacity compared to both RC and FRC counterparts. A single degree of freedom model was adopted to analyze the global flexural behavior of RC and ECC panels.

This study concentrates on experimental evaluation of the effect of fiber reinforcement on the bond response of steel bars under load reversals. Beam specimens with symmetrical spliced top and bottom steel bars were used in the investigation. The specimens were designed to experience splitting mode of bond failure. The test variables included the diameter of the spliced reinforcement $d_b$ or the ratio of concrete cover to bar diameter $c∕d_b$ , the concrete compressive strength: normal-strength concrete (NSC) and high-strength concrete (HSC), and the volume fraction of steel fibers. Without fiber reinforcement, the control specimens experienced very sudden and quick bond deterioration leading to a total loss of load resistance in the first cycle following bond splitting. The presence of steel fibers increased the peak bond strength, reduced the bond degradation or damage under cyclic loading, and resulted in substantially enhanced energy absorption and dissipation capacities. The level of improvement in cyclic performance increased with increase in $c∕d_b$ . Also, the increases in average bond strength at bond failure due to fibers were higher for the HSC when compared to the NSC specimens. Design equations in which the bond strength is expressed as a function of ${f_c^{\prime }}^{1∕4}$ were more accurate in predicting the test data for the plain unconfined specimens in comparison with ${f_c^{\prime }}^{1∕2}$ . Available expressions for predicting the bond strength of developed/spliced bars in fiber-reinforced concrete showed good agreement with the test results.

A laboratory study has been carried out to develop mechanical models for the dynamic modulus, fatigue life, and rutting performance of asphalt concrete as a function of air void content. The experimental program includes an axial compression complex modulus test, indirect tensile (IDT) fatigue test, and triaxial repeated load permanent deformation (TRLPD) test on the two most commonly used asphalt–aggregate mixtures in North Carolina. The dynamic moduli are determined using axial compression tests with and without confining pressure, and the results are compared to evaluate the effect of confining pressure on the dynamic modulus. The relationship between the dynamic moduli that are determined from the uniaxial compression test and the air void content is developed. The growth of the tensile strain and axial permanent strain is measured from the IDT fatigue test and TRLPD test, respectively, and is used to determine the fatigue life and rutting behavior of the mixtures. The fatigue and rutting models adopted in the new NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide have been refined to represent the IDT and TRLPD test results more accurately and to incorporate the air void content as an input parameter.

The most commonly used method of measuring the fracture energy, $G_F$ , is the method proposed by RILEM TC-50. Although this procedure is widely examined for plain concrete, its applicability to steel-fiber-reinforced concrete (SFRC) needs further evaluation. In this paper, in addition to the RILEM specimen of the three-point bend test, a cylindrical test specimen is also examined. All cylindrical-beam specimens had $300\text{-}\mathrm{mm}$ length, with $250\text{-}\mathrm{mm}$ span, and $150\text{-}\mathrm{mm}$ diameter. The same molds of standard compression tests were used to cast the SFRC specimens. Steel fibers were crimped and had an average length of $32\mathrm{mm}$ . Fibers had an average tensile strength of $600\mathrm{MPa}$ and the apparent modulus of elasticity of $200\mathrm{GPa}$ . Results obtained from this study were compared with other experimental results on notched beams. The results of the cylindrical specimens were very close to the results of the beams with rectangular cross section. The effect of the volumetric fraction of fibers in SFRC on the $G_F$ for three low-percent-volume fractions of steel fibers, 0.5, 1, and 1.5%, was examined. The values of $G_F$ increased about 11, 15, and 21 times when fiber volume fraction of 0.5, 1, and 1.5% were added to plain concrete, respectively. The cylindrical beams also could be used for the evaluation of existing materials by drilling the structure and obtaining cylindrical cores. By means of linear elastic fracture mechanics analysis it was found that, the minimum depth of initial notch in cylindrical specimen should be greater than 10% of the diameter to ensure geometrical unstable crack growth. Moreover, a new trilinear cohesive law, which predicts both the peak-load and the postpeak behaviors more accurately than the bilinear cohesive law, is proposed.

Cement-treated aggregate (CTA) is commonly used to provide a stable base for pavements that are placed over weak soil subgrades. Because CTA reduces the thickness of the aggregate required to provide a durable base by approximately one-half, using it as a bearing layer for pavement can limit the quantity of unsuitable soil that must be excavated and removed, and can reduce the erodability of the stabilized soils. However, the field performance of CTA is variable, even when prepared according to set standards. This laboratory-based investigation explored the effects of fines content, cement content, mineralogy, pH, and freeze/thaw cycling on the unconfined compressive strength of cement-treated aggregate. The mineralogy of the base aggregate was found to make a significant difference in the strength of the CTA, with strength increasing in the following order: mica, limestone, and diabase. The granite aggregate yielded variable results, but the strengths were generally on the order of those determined for the diabase aggregate. The pH of the samples also correlated well, with the measured strengths increasing as the pH increased. As was anticipated, increasing the cement content increased the measured unconfined compressive strength of cylinders that were not subjected to freeze/thaw cycling. The same basic trend was observed in cylinders that were subjected to freeze/thaw cycling; however, the increase was less pronounced in the cylinders that were subjected to physical abrasion during thaw cycles. The fines content did not significantly influence the unconfined compressive strength of the cylinders that were not subjected to freeze/thaw cycling; however, the fines content appeared to confer a protective effect to the durability of the cylinders that were subjected to freeze/thaw. For the freeze/thaw test conditions (with and without physical abrasion), the unconfined compressive strength increased as the fines content was increased.

The commonly used Pauw’s formula to predict elastic modulus of concrete is very general and does not address the complexity of modern concretes, such as high-strength concrete, use of different types of aggregates and admixtures, etc. This paper develops a statistical framework to construct probabilistic models for the elastic modulus of concrete and evaluates the influence of different aggregate types, based on a large number of experimental data. The proposed framework to construct probabilistic models expands upon Pauw’s formula and properly accounts for both aleatory and epistemic uncertainties. Bayesian updating is used to assess the unknown model parameters based on experimental data. A Bayesian stepwise deletion process is used to identify important explanatory functions and construct parsimonious models. As an application, the approach is used to develop a probabilistic model for concretes made using crushed limestone and crushed quartz schist coarse aggregates.

The work reported in this paper is based on a laboratory study of superplasticized high-volume fly-ash (HVFA) concrete suitable for pavement construction. Three control concrete mixtures having $400\mathrm{kg}∕{\mathrm{m}}^3$ of ordinary portland cement (OPC) and water–cementitious material (w–cm) ratios of 0.30, 0.34, and 0.40 were prepared. Other concrete mixtures were then prepared by substituting 20, 30, 40, 50, and 60% fly ash in all control mixtures. Compressive and flexural strengths at ages of 7, 28, 90, 180, 256, and 365 days, drying shrinkage, and abrasion resistance of concrete were measured for all the mixtures. The laboratory test results showed that HVFA concrete mixtures containing 50–60% fly ash can be designed to fulfill the requirement of strength and workability suitable for cement concrete pavement construction. At all w–cm ratios, the concrete mixture containing 60% OPC and 40% fly ash developed maximum strength at the age of 90 days and beyond. However, a maximum increase in the strength of concrete at 365 days over the 28 days strength was observed in the mixtures containing equal amount of OPC and fly ash. Drying shrinkage of concrete decreased with decreasing w–cm ratio and increasing fly-ash content. Among all the concrete mixtures, the mixture with w–cm ratio of 0.30 and containing 60% fly ash showed least shrinkage. Abrasion resistance of concrete, measured by the sand-blasting method, decreased with increasing fly-ash content and decreasing compressive strength. However, abrasion resistance of HVFA concrete mixture with 60% fly ash at $0.30\mathrm{w}–\mathrm{cm}$ ratio was adequate from concrete-pavement considerations.

Asphalt mixes exhibit a viscoelastic-viscoplastic behavior, and the contribution of the different constitutive components depends on the temperature and rate of loading. This paper presents an anisotropic nonlinear viscoelastic-viscoplastic model for asphalt mixes. The influence of the anisotropic aggregate distribution is accounted for in both the viscoelastic and viscoplastic responses. The model’s parameters were determined based on the analysis of repeated creep triaxial tests on three asphalt mixes that included aggregates with different characteristics. The paper discusses the experimental factors that need to be considered in conducting the repeated creep tests in order to determine the model’s viscoelastic and viscoplastic parameters. It also discusses the relationship between these parameters and mix properties. The results show that the mix nonlinear viscoelastic response, hardening, dilation or contraction behavior, and damage depend on aggregate properties.