Journal of Materials in Civil Engineering

The maturity method accounts for the effect of curing temperature on the strength development of well-cured and consolidated concrete. This paper describes an investigation of the accuracy of the maturity method to estimate the strength when different cementitious systems are used. Mortar cubes, made from Type I cement and various replacement levels of Class C fly ash, Class F fly ash, and ground-granulated blast-furnace slag, were cured at isothermal curing temperatures of 8, 23, and $40°\mathrm{C}$ . The amount of long-term strength reduction, due to curing at high temperatures compared with curing at room temperature, is influenced by the type of cementitious system used in the concrete mixture. Based on the strength results of these mortar cubes and the procedure outlined in ASTM C 1074, datum temperature and activation energy values were determined for these cementitious systems. The ability of the equivalent age maturity method to accurately estimate the strength is significantly influenced by the composition of the cementitious material system.

The most common test to evaluate the representative modulus and nonlinear behavior of base and subgrade materials is the resilient modulus test. Due to the comprehensive nature of the method, the preparation and testing of one specimen may take up to $6\mathrm{h}$ . For field quality control, a more rapid method of determining the in-place modulus is desirable. One way to achieve this goal is through in situ seismic methods. However, since the seismic tests provide small-strain moduli whereas the resilient modulus tests measure moduli at higher strains, some additional considerations must be taken into account to relate these two moduli. This paper presents some possibilities for relating these tests in a rational manner.

To calculate the shear capacity of structural members reinforced with fiber-reinforced polymer (FRP), current shear design provisions generally use slightly modified versions of existing semiempirical shear design equations initially developed for steel reinforced concrete beams. Such methods generally assume that the traditional approach of superimposing concrete contribution to shear, $V_c$ to that of stirrups, $V_s$ can also be used to calculate the nominal shear capacity, $V_n$ of FRP-reinforced concrete beams provided that the axial rigidity of FRP longitudinal bars and the capacity of FRP stirrups at the bent portions are accounted for. These methods also noticeably vary in the manner they account for the effect of basic shear design parameters on shear strength. This paper presents simple yet improved equations to calculate the shear capacity of FRP-reinforced concrete beams based on the genetic algorithms approach. The performance of the proposed equations is compared to that of four commonly used shear design methods for FRP-reinforced concrete beams, namely the ACI 440, CSA S806, JSCE, and ISIS Canada. Results show that current guidelines are either inadequate or very conservative in estimating the shear strength of FRP-reinforced concrete beams. Moreover, the shear capacity of FRP-reinforced concrete beams calculated using the proposed equations is in better agreement with available experimental data than that calculated using shear equations provided by current provisions. This study also shows that the axial rigidity of FRP longitudinal bars is best represented by a cubic root function and that the contribution of FRP stirrups to shear strength is a square root function of the stirrups ultimate capacity rather than a linear function as proposed by current shear provisions.

Two types of polyethylene are used for pipeline systems: medium density polyethylene and high density polyethylene. A polyethylene pipe, being a thermoplastic, softens on heating and hardens on cooling. Because of the viscoelastic nature of polyethylene, stresses decrease under applied constant strain and strains increase under applied constant stress. To account for the complex behavior of polyethylene pipe, laboratory tests were performed to study its thermal and mechanical properties. This paper presents the test results, findings, and design recommendations for polyethylene pipe properties. The tests were performed in a temperature controlled room, where properties were investigated for thermal variations expected in the field. Two types of tests were performed: stress relaxation tests and temperature ramp tests. Test methods and properties are summarized for relaxation modulus, instantaneous modulus, Poisson’s ratio, thermal expansion/contraction coefficient, and stress relaxation rates.

In the interest of increasing allowable limits of microfine $(<75\mu \mathrm{m})$ aggregates in concrete, it is important to understand the effects of ultrafine particles $(\sim 5\mu \mathrm{m})$ on concrete performance, including those of clay and nonclay mineralogy. The present study examines both of these types of ultrafine particles. The former may be present in natural aggregates and the latter are prevalent in manufactured fine aggregate. The effects on workability, compressive strength, and drying shrinkage are examined. Additionally, a method of mitigating the adsorptive capacity of clays is investigated.

Due to the availability of a wide variety of repair materials in the industry with a wide range of physical and mechanical properties, it is important to determine the compatibility of a repair material with the substrate concrete. In this paper, the writers investigate the compatibility between selected cementitious repair materials and a substrate concrete using a modified ASTM C 78 test procedure. The flexural strength and load-deflection curves of composite beams prepared with substrate concrete and repair materials were compared to the results from the substrate beam to assess the compatibility. In addition, the influence of three different types of curing conditions was evaluated on the compatibility between the repair materials and substrate concrete. Compressive strength, flexural strength, split tensile strength, and drying shrinkage of the repair materials and substrate concrete were individually measured to aid in the analysis of compatibility between repair and substrate materials. It was observed that not only did significant differences in strength between the repair material and substrate concrete cause incompatible failures, but high drying shrinkage of the repair materials was also found to cause incompatible failure. These findings validate previous research findings.

This paper reports on a study of waste clay brick that was ground and used as a supplementary cementitious material (SCM) in a mortar. The effect of this ground brick, in comparison with other conventional pozzolanic materials (namely, a Class F fly ash, and a natural pozzolan), on the alkali–silica reaction (ASR) of the mortar was evaluated. The ground clay brick, fly ash, and natural pozzolan were introduced into the mortar as a cement replacement at a 20 or 35% level. Fly ash–natural pozzolan and fly ash–ground clay brick combinations were also employed as a cement replacement at a 35% level. These SCM-incorporated mortar samples were tested for ASR expansion, flexural and compressive strength, and rapid chloride permeability. The test results indicate that all the SCMs considered in this study reduced the mortar ASR expansion, rapid chloride permeability, and the ASR-associated strength loss. The finely ground waste clay brick demonstrated high potential to reduce the ASR expansion as well as the ASR-associated strength loss.

The compaction conditions (e.g., compaction temperature and compaction level) of crumb rubber modified (CRM) asphalt mixtures should be determined carefully because the viscosity and amount of the CRM binder affects the compactability of the mixtures. Furthermore, the properties of CRM mixtures relating to the compaction conditions have not been studied in great detail. In this study, a laboratory investigation was conducted on the volumetric and rutting properties of CRM mixtures as a function of compaction conditions. For this research work, four Superpave mix designs for four different asphalt binders (control, SBS modified, 10% rubber modified, and 15% rubber modified) were carried out to determine the optimum asphalt contents. A total of 260 specimens were fabricated using the Superpave gyratory compactor at four compaction temperatures (116, 135, 154, and $173°\mathrm{C}$ ) and five compaction levels (20, 40, 60, 80, and 100 gyrations). The volumetric properties were obtained and analyzed, and the rutting resistance of the mixtures was measured using the asphalt pavement analyzer. The results from this study indicated that: (1) the compaction temperatures used in this study significantly affected the volumetric properties of the CRM mixtures, unlike the control and SBS-modified mixtures; (2) in general, the air void contents of the mixtures were significantly influenced by the compaction levels; and (3) as expected, the higher air void contents of the CRM mixtures seemed to have a detrimental effect on the rutting resistance.

The construction of reinforced concrete structures in hot weather dictates fast placement of fresh concrete to prevent hot weather concreting difficulties such as rapid loss of workability, pumping problems, acceleration of cement hydration, fast evaporation of mixing water, and forming of cold joints. In this process, the selection of adequate chemical admixtures is of paramount importance. In the current study, the viscoelastic properties of portland cement pastes with a water–cement ratio $(w∕c)$ of 0.35 and 0.50 were investigated at different temperatures in the range of $20–45°\mathrm{C}$ through oscillatory rheological tests conducted using an advanced shear-stress/shear-strain controlled rheometer. The influence of water reducing and retarding admixtures, melamine-based, polycarboxylate-based, and a new generation of polycarboxylate-based high-range water reducing admixtures on the oscillatory rheological properties of cement paste at various temperatures was also examined. The results indicate that the viscoelastic properties of cement paste are highly affected by the admixture type and dosage, and that an improved understanding of the effect of chemical admixtures is needed to mitigate high-temperature concreting problems.

This technical note documents an experimental study conducted to examine the time-dependent mechanical response of specimens composed of sand and granulated tire rubber, loaded in one-dimensional compression. The results indicate that sand–rubber creep is significant and may be reasonably estimated with the use of an available soil creep model. The swelling of granulated tire rubber due to oil absorption reveals the potential for its use as a stabilizing engineering material.