Journal of Materials in Civil Engineering

The compressive strength of mass concrete in dams is obtained from laboratory experiments of various cylindrical specimens with diameters of 150, 250, and $300\mathrm{mm}$ , and heights of 300, 500, and $450\mathrm{mm}$ , respectively. These specimens with 37.5, 75, and $150\mathrm{mm}$ maximum size of aggregate were investigated. The 7- and $90\text{-}\text{day}$ compressive strength of concrete was found to be between 20 and $58\mathrm{MPa}$ depending on the size of the specimens. The results reveal the existence of a significant size effect. Based on test results, relationships between the strength of mass concrete specimens and their size and shape are developed. Finally, results and a discussion are presented regarding compressive strength gain with time, effect of maximum aggregate size $\left(d_a\right)$ , and specimen size effect.

Fly ash is normally solidified by strong alkaline solutions at room or moderate temperatures. In this study, an innovative process of recycling fly ash (both Class F and Class C) into potential construction materials with superior mechanical properties is investigated. This innovative process involves chemical activation, hydrothermal reaction (hence, heat and moisture), and hot pressing. The emphasis is on the synergistic effects. Several key parameters—such as treatment temperature, duration of process, and amount of chemical activator—are evaluated critically. The results confirm that fly ash can be solidified and specimens show splitting tensile strengths of about $1.0\mathrm{MPa}$ by hydrothermal hot pressing alone. With a small amount of chemical activator (NaOH), the tensile strength can reach as high as $5.4\mathrm{MPa}$ .

The influence of low temperature curing on the performance of concrete containing metakaolin (MK) is investigated. Portland cement was partially replaced with 0–30% MK. The water to binder ratio was maintained at 0.5 for all mixes. Concretes were subjected to water and air curing at $5°\mathrm{C}$ . Compressive strength was conducted on water cured specimens whereas, ultrasonic pulse velocity and length change were conducted on water and air cured specimens. During the first day of hydration, the concrete strength is substantially reduced especially at high MK content. However, the incorporation of up to 20% MK causes an enhancement in concrete strength beyond $7\text{days}$ of curing. This increase could be up to 50% depending upon the age of curing and the MK content. After $28\text{days}$ of curing the relative strength continues to increase. This finding is compared with results obtained in a previous investigation for MK concrete cured at $20°\mathrm{C}$ and analyzed using the maturity method. The incorporation of up to 15% MK causes an increase in linear shrinkage. Beyond 20% MK, the shrinkage is reduced.

The new understanding for the hydration mechanism of cement has been achieved based on the noncontact electrical resistivity measurement. The cement hydration process is divided into dissolution, dynamic balance, setting, hardening, and hardening deceleration stages according to the characteristic points on the electrical resistivity development curve $\rho \left(t\right)-t$ and the differential curve $d\rho \left(t\right)∕dt-t$ . The microstructure analysis corresponding to each hydration stage is conducted with scanning electron microscope, x-ray diffraction, differential thermal analysis, and Fourier transform infrared spectroscopy techniques. This study provides the theoretical foundation for understanding the relationship between setting behavior, hardening properties, and resistivity development.

Studies since the early 1990s have been conducted in Texas to gain a better understanding of mechanisms, material properties, and construction practices related to early-age delamination in continuously reinforced concrete pavements made with gravel aggregates. However, information was still needed on: (1) the individual and overall effects of aggregate and nonaggregate factors on the early-age delamination; and (2) how the interfacial transition zone (ITZ) affects the early-age bond strength in terms of these factors. In this research, the effects of key material and construction factors including aggregate type, water-cementitious ratio, ultrafine fly ash content, and curing method were investigated through laboratory studies. A rating system based on utility theory was proposed to represent the overall aggregate effect through proper weighted contribution of its individual physical, geometric, and chemical characteristics. The investigation of possible corrective measures to minimize early-age delamination was conducted and results were presented. Petrographic analysis through selective ITZ investigation was undertaken to verify laboratory research findings.

The recycling of hot-mix asphalt pavements containing a crumb rubber modifier (CRM) has been an area of interest since CRM was first used in asphalt paving materials over $40\text{years}$ ago. Studies on the recycling of rubberized asphalt concrete materials have focused mainly on the mixture properties at the location of in-field paving. However, for the long-term performance characterizations, there is a need to investigate the aging properties of rubberized binders and the subsequent recycling properties of these aged rubberized binders. To address this issue, the previous research was conducted to identify performance properties of recycled aged CRM binders using Superpave binder test methods. The research results indicated that the recycled aged CRM binders can result in satisfactory binder performance meeting current Superpave binder requirements. This paper presents a limited study that uses gel permeation chromatography (GPC) to characterize the aging process of recycled aged CRM binders as a function of binder source and RAP binder percentage. In addition, performance properties of the binders at three aging states (i.e., original, RTFO residual, and $\mathrm{RTFO}+\mathrm{PAV}$ residual) were correlated with the large molecular size (LMS) values from the GPC results. The results indicated that the compositional changes of recycled aged CRM binders are well reflected by the GPC parameter (i.e., LMS), and the performance properties from Superpave binder tests have good correlations with the corresponding LMS values. In addition, the empirical prediction models for long-term performance properties were developed using the GPC parameter and physical properties of the binders. The predicted values showed a high correlation with the performance properties of $G^{*}\sin \delta$ and stiffness of binders.

The time-dependent rheological behavior at high temperature of cement paste incorporating various chemical admixtures is critical for hot-weather concreting applications. This paper investigates the combined effects of temperature and time on the performance of polycarboxylate-, melamine sulfonate- and naphthalene sulfonate-based high-range water-reducing admixtures used to enhance the flow of cement paste. Rheological parameters, including yield stress, plastic viscosity, and thixotropy of cement pastes with a water/binder ratio of 0.38, were measured as a function of the superplasticizer dosage and temperature $(22–45°\mathrm{C})$ from $20\text{to}110\min$ from the time of mixing with $30\min$ between successive measurements. The rheological tests were conducted using an advanced shear-stress/shear-strain controlled rheometer. This paper aims at developing a better understanding of the coupled time and temperature effects on the performance of various superplasticizers, and formulating more realistic recommendations for using such admixtures in hot weather. Current technical information on chemical admixtures used in concrete has traditionally been developed in countries with mild climates and is often unreliable when transposed to extreme weather conditions. Thus, the findings of this study should have significant implications in practice. Results indicate that polycarboxylate-based superplasticizers should be used at a dosage close to the saturation in order to ensure adequate rheological behavior at high temperature and prolonged mixing time, while melamine sulfonate- and naphthalene sulfonate-based superplasticizers should be used at dosages beyond the saturation level.

In this experimental study, the influence of using fly ash, polypropylene fiber, and steel fiber in concrete on abrasion resistance is presented. Seven concrete mixtures containing 0, 10, 15, 20, 25, 30, and 45% fly ash as cement replacement in mass basis were prepared. Another, seven fiber-reinforced portland cement concrete mixtures containing 0.25, 0.5, 1, and 1.5% steel fiber, and 0.05, 0.1, and 0.2% polypropylene fiber in volume basis were prepared. These seven fiber-reinforced Portland cement concrete mixtures were modified by replacing 15 and 30% fly ash with cement in mass basis, consequently, 14 fiber-reinforced fly ash concrete mixtures were prepared. Water-binder ratio was kept constant at 0.35 for all concrete mixtures. Bohme surface abrasions of the concrete mixtures were measured at $28\text{days}$ . The results of the laboratory work showed that replacement of fly ash with cement reduced abrasion resistance of concrete; however, inclusion of the steel fiber improved the abrasion resistance of concrete. Using polypropylene fiber did not improve abrasion resistance of concrete made with or without fly ash. The comparison between the relation of abrasion to compressive strength and abrasion to flexural tensile strength, made in terms of $R^2$ of the linear regression on log scale, showed that a stronger relation existed between abrasion and flexural tensile strength than between abrasion and compressive strength of the concrete containing either fly ash or fibers, or both.

The warm-mix asphalt (WMA) refers to technologies that allow a significant reduction of mixing and compaction temperatures of asphalt mixes through lowering the viscosity of asphalt binders. Several studies have been carried out evaluating the properties of WMA, and it is found that warm mix additives work in different ways either in reducing the viscosity of the binder or allowing better workability of the mix at lower temperatures. In terms of rubberized asphalt mixtures, they are generally produced and compacted at higher temperatures than conventional mixtures, based on the field experience. If the technologies of warm-mix asphalt are incorporated, it is expected to reduce the mixing and compaction temperatures of rubberized asphalt mixtures to those of conventional mixtures. This study was initiated to investigate the effects of compaction temperature on rubberized mixes containing the warm mix additives. For this, four Superpave mix designs for two asphalt binders and two aggregate sources were conducted to determine optimum asphalt contents. Warm rubberized mixes were produced using two of the available processes. A total of 192 specimens (4 mix types: control mix, rubberized mix, warm rubberized mix 1, and warm rubberized mix $2\times 2$ aggregate sources $\times 4$ compaction temperatures: 97, 116, 135, and $154°\mathrm{C}\times 6$ repetitions) were fabricated using Superpave gyratory compactor. Volumetric properties of the specimens were evaluated. The results showed that the warm mix processes were effective to improve the volumetric properties of rubberized mixes at a certain range of compaction temperatures.

The indirect tension test has received extensive attention due to its capability to test field cores from thin asphalt layers. For that reason, the fundamental viscoelastic material property, creep compliance, or complex modulus has been determined by employing the indirect tension testing system. However, if the creep compliance or complex modulus is to be determined from such a multiaxial testing mode, another crucial material property must be introduced, that is, Poisson’s ratio. It is well known that the Poisson’s ratio of a viscoelastic material is a function of time or frequency; nevertheless, it has been commonly assumed to be a constant and a time- or frequency-independent property. In this study, computation algorithms for determining the time- and frequency-dependent Poisson’s ratio of asphalt mixtures were developed based on the theory of viscoelasticity. From the comparative study, it was found that the Poisson’s ratio determined from the frequency domain corresponded well to that determined from the time domain. Further study performed on the sensitivity of Poisson’s ratio clearly showed that the time-dependent Poisson’s ratio was an important property in determining accurate creep compliance, and an inappropriate assumption for Poisson’s ratio overestimated or underestimated the measured creep compliance.

This research aims to utilize palm oil fuel ash (POFA) as a pozzolanic material for replacing portland cement. POFA was ground by ball milling until the median particle sizes were 19.91 (G1P) and $10.18\mu \mathrm{m}$ (G2P). portland cement Type I was replaced by all POFA of 10–40% by weight of the binder. The effects of POFA fineness on the setting times, compressive strength, and expansion of mortars exposed to a 5% $\mathrm{Mg}\mathrm{S}{\mathrm{O}}_4$ solution were investigated. It was found that the use of POFA to replace portland cement Type I caused an increase in water demand for normal consistency and setting times, depending on the fineness and level replacement of POFA. With 10% replacement of portland cement Type I by G1P or G2P, the compressive strengths of the POFA mortars were 102–104% of that of portland cement Type I mortar at $90\text{days}$ . For sulfate resistance, the expansions at $1\text{year}$ for all mortar bars containing G1P or G2P were less than those of mortar bars made from portland cement Types I and V. The results suggest that ground POFA is a good pozzolanic material and can be used to increase both the compressive strength and the sulfate resistance of mortar.