Journal of Materials in Civil Engineering

For use in fire resistance calculations, the relevant thermal properties of high-strength concrete (HSC) were determined as a function of temperature. These properties included the thermal conductivity, specific heat, thermal expansion, and mass loss of plain and steel fibre-reinforced concrete made of siliceous and carbonate aggregate. The thermal properties are presented in equations that express the values of these properties as a function of temperature in the temperature range between 0 and 1,000°C. The effect of temperature on thermal conductivity, thermal expansion, specific heat, and mass loss of HSC is discussed. Test data indicate that the type of aggregate has a significant influence on the thermal properties of HSC, while the presence of steel fiber reinforcement has very little influence on the thermal properties of HSC.

This paper develops the specification of a short tensile coupon (<60 mm long) through numerical modeling to negate Poisson’s effects in the accurate determination of elastic material properties and strength for pultruded glass-reinforced plastic (GRP) structural sections, the geometries of which prevent the extraction of a standard length coupon. Effects of geometric parameters including the ratio of orthotropy, coupon length, gauge length, thickness, and clamping length are presented. The validity and application of a “short” coupon is demonstrated through an experimental program to characterize the orthotropic tensile properties of the pultruded GRP box section in the longitudinal and transverse directions and the isotropic (assumed) elastic properties of a GRP connector. Initial tests have been conducted using ASTM D 3039 specimens to provide the longitudinal tensile properties of the pultruded GRP box section. Proposed “short” coupons have been extracted from the same parent material (location and direction) to enable a comparison with the properties obtained from the standard methodology. Transverse tensile properties of the pultruded GRP box section and the tensile properties of the GRP connector have been determined using the “short” coupon. With regard to the GRP connector, comments are made correlating observed material property variations and the influence of the manufacturing process.

This paper contains a discussion on the practice and recommendations of placing RCC (roller-compacted concrete) during cold weather in a mass-concrete applications, such as in an RCC dam or RCC buttress for a dam. When cold weather placement conditions are anticipated for a particular project site, it is possible to incorporate into the design and construction quality control provisions that would minimize the adverse effects of cold weather on the RCC. This paper provides a practical approach whereby the contractor is allowed to produce and place RCC during cold weather without sacrificing the quality and design intent of the material. Three case histories are presented to illustrate the construction problems and performance of RCC placed under cold weather conditions. Guide specifications are also provided for cold-weather RCC placement.

The measurement of internal strain with a fully noninvasive method should allow us to obtain very useful information, both in laboratory testing and in structural monitoring. Fiber optic sensors are suitable for this purpose because of their very small dimensions. Various applications of fiber optic strain sensors to concrete are available in the literature. This paper reports two applications in particular. The first is aimed at measuring the transversal strain in the core of concrete cylinders subject to compressive tests, avoiding any disturbance to the stress state, and the second deals with reinforced concrete beams externally strengthened with sheets of fibrous composite material. In the latter case, the writers attempt to measure the concrete strain at the interface in order to compare it with the strain of the composite. In both cases, specific procedures were developed to properly place the sensors, avoiding any damage. The performance of fiber optic sensors embedded in concrete specimens was very good and allowed us to achieve a reliable measurement of the transversal strain and Poisson's ratio. The strain measurements at the concrete-FRP interface showed that this technique is promising and can improve the knowledge of the strain state at a debonded region.

This study deals with the carbonation of concrete incorporating ground granulated blast-furnace slag (GGBS), fly ash (FA), and silica fume (SF). It is observed that a decreased water-to-binder ratio and replacement level of GGBS, FA, or SF, or an increase in GGBS fineness and curing age in water, led to better carbonation resistance. However, compared to a plain concrete, the concrete incorporating mineral admixtures (except GGBS with higher fineness and SF) generally showed lower resistance to carbonation, possibly due to the dominating effect of the reduction in calcium hydroxide over pore refinement. Hence, adequate curing is recommended for enhancing the resistance of concrete containing GGBS, FA, and SF to carbonation. It is also found that both the carbonation coefficient and compressive strength served as good indicators for the carbonation rate of concrete with and without mineral admixtures.

An experimental investigation of the durability of natural and polymer-amended Boston Blue Clay (BBC) used in waste containment applications was conducted. Durability was assessed in terms of hydraulic conductivity and crack formation in response to freeze-thaw- and desiccation-induced stresses. The polymers tested were nonionic polysaccharide (guar gum) and cationic polyacrylamide (PAM) with aqueous concentrations ranging from 0.25 to 8.00 g/L. BBC proved resistant to shrinkage cracks from desiccation, but susceptible to ice lensing from the application of freeze-thaw cycles. The saturated hydraulic conductivity of natural BBC increased from 5×10⁻⁵ to 1×10⁻³ cm/s after five freeze-thaw cycles. The saturated hydraulic conductivity for guar- and PAM-amended BBC also increased in response to freeze-thaw cycling; however, both the initial and final values were nearly an order of magnitude lower than those of natural BBC. In terms of crack formation as identified with computed topography scans, extensive ice lensing was observed in both the unamended and guar-amended specimens, while the PAM-amended specimen exhibited no such behavior in response to freeze-thaw cycling. Crack formation from either desiccation or freeze-thaw cycling was quantified in terms of a crack area density (CAD) that decreased for both guar- and PAM-amended specimens, as compared with the natural BBC. In particular, the observed CAD values for natural and PAM-amended BBC subjected to freeze-thaw cycling were 69 and 8%, respectively. The observed CAD values for all BBC specimens subjected to desiccation stress were less than 3%. Overall, these results indicate that natural BBC may be unsuitable for waste containment applications where control measures are not implemented for frost penetration. Moreover, polymer amendment serves to improve the material by reducing crack formation and hydraulic conductivity.

In this work, a laboratory investigation was carried out to evaluate the strength and particularly the shrinkage properties of concrete containing high volumes of fly ash. The concrete mixtures made with 50 and 70% replacement (by mass) of ordinary portland cement (OPC) with fly ash were prepared. Water-cementitious material ratios ranged from 0.28 to 0.34. Some concrete mixtures were also made with superplasticizer. The strength and shrinkage properties of the concrete mixtures cured at 20°C temperature with 65% relative humidity are reported. The laboratory test results show that high-volume fly ash (HVFA) concrete attained satisfactory compressive and tensile strength at 1 day of age. It also showed that 50% replacement HVFA concrete developed higher strength than OPC concrete at 28 days and beyond. The inclusion of high volumes of fly ash in concrete with a low water-cementitious material ratio resulted in a reduction in the shrinkage values of up to 30% when compared to OPC concrete. The concrete mixtures made with superplasticizer showed higher shrinkage values of up to 50% when compared to the concrete made with no superplasticizer.

Fourier transform infrared spectroscopy by attenuated total reflectance (FTIR-ATR) has been applied to laboratory studies of bitumen rejuvenator diffusion. Previous studies have given more indications rather than a real understanding of the mechanisms involved. FTIR-ATR can be performed in a relatively easy manner to provide diffusion measurements. In this study, parameters such as temperature, binder film thickness, type of bitumen, and, to some extent, chemical properties of the binders have been investigated. The results show a major influence of temperature on the diffusion rate. The study also shows that the diffusion process can be described using Fick’s law. The need for a paper on this topic emanates from the lack of knowledge regarding the diffusion process by which new and old binders are mixed during asphalt recycling. If the process is incomplete, the properties of the final recycled asphalt will be influenced negatively. Further research is required to better understand the process of diffusion in bituminous binders. This can be accomplished by testing other combinations of binders, aged and unaged, as well as by studying the diffusion of selected chemical substances (markers) into bitumen.

A cold mix design procedure was developed to incorporate hydrocarbon-contaminated soil as an ingredient of pavement base-product. The incorporation was achieved by asphaltic stabilization and encapsulation utilizing cold mix asphalt technology. The main focus is to maximize the soil in economically viable end products that meet industry standards, engineering requirements, and environmental safety requirements. Mix design was performed by several trials based on bench-scale parameters. Aggregate from a local quarry was used as one of the ingredients of mix to reduce end product cost. Soil and aggregate, prior to their incorporation, were assessed for their suitability for use in the stabilization process by bench-scale tests such as particle size distribution, sand equivalent, plasticity, density, and specific gravity. Varying amounts of affected soil, aggregate, a small amount of portland cement, and specified grades of emulsion were mixed, compacted, and tested for resistance and tensile strength. Leachate testing of the engineered product for total hydrocarbon ensured its use in a pavement base. The formulated mix design incorporated 80% of the hydrocarbon-affected soil by weight of soil-aggregate mix. Incorporating a higher percent of soil in the mix can lose the economic incentive because of the increased cost of emulsion.

Fiber-reinforced concrete used in structural applications requires characteristic material properties that can be easily incorporated into existing design procedures. This paper investigates the postcracking response of reinforced concrete tension members made with both plain and steel fiber-reinforced concrete (SFRC). Loading was either monotonic or cyclic, and shrinkage effects are included in analysis of the member response. Tension-stiffening results are used to determine the average tensile response of concrete after cracking, and an expression is developed to predict this smeared behavior as a material property for cracked SFRC, as well as to estimate crack spacings. Specimens with steel fibers exhibited increased tension stiffening and smaller crack spacings, which both contributed to a reduction in crack widths. The postcracking tensile strength of fiber concrete at the cracks is the determining factor affecting behavior and is a fundamental material property used to predict tension stiffening and crack behavior for conventionally reinforced SFRC. The uniaxial strength of SFRC immediately after cracking governs serviceability behavior, while the postcracking strength at larger deformations governs strength design and is responsible for tension stiffening after yielding of the reinforcement. Cyclic loading did not have a significant effect on either tension stiffening or crack width control for the specimens tested.

The two governing equations that describe the diffusion of chloride ions into nonsaturated concrete are established. Material models for the four material parameters involved in the governing equations are developed, including chloride binding capacity, chloride diffusion coefficient, moisture capacity, and moisture diffusion coefficient. The planned attempt is to establish material models based on analytical results first, and if this is not possible, to develop empirical models based on dominant physical or chemical mechanism(s) at different scale levels and calibrate the individual model by related test data. The alternating-direction implicit (ADI) finite-difference method was employed for solving coupled two-dimensional moisture diffusion and chloride penetration equations. The numerical solutions are compared with the experimental results obtained by the 90-day ponding test (AASHTO T259-80). The numerical prediction agrees very well with the test data. Free chloride concentration profiles at different depths and different ages of concrete slab are presented. Two limiting cases for different initial relative humidity levels are analyzed in detail to study the dependence of the chloride diffusion on the moisture diffusion in nonsaturated concrete.

There is growing interest in the effect of processing methods on the properties of cement composites. The present work compares two processing methods: casting and extrusion. The effects of high fly-ash content (70% by volume, replacement of cement) and different fiber lengths on the mechanical properties and microstructure characteristics are examined. Opposing trends are observed between the cast and the extruded composites. Increasing fiber length improves the mechanical behavior of cast composite, but it reduces the behavior of extruded composite (without fly ash). The use of fly ash had a negative effect on the mechanical performance of cast products, but a positive effect on the performance of extruded products (with long fibers). This contradictory behavior was explained by the differences in bond strength and matrix properties in the different systems, changing the mode of failure from fiber pullout to fiber fracture. It was concluded that the extrusion process improves the mechanical performance of cement composites. To achieve such improvement the properties and geometry of the fibers as well as the material ingredients and proportions should be chosen carefully and properly controlled.

The results of nondestructive testing of mortar specimens using a simple and inexpensive microwave measurement system are presented. Temporal dependencies of amplitude of reflection and transmission coefficients at x band for the specimens made with different water-to-cement ratio (w/c) are given. It is shown that there is a strong correlation between the measured results and w/c. The results also demonstrate the influence of curing conditions and the effects of aging.

This technical note discusses an innovative use of maize-cob ash (MCA) as a filler in concrete. MCA in the range of 0–30% was used as a partial replacement for ordinary portland cement in a concrete of mix ratio 1:2:4:0.6 (cement:sand:coarse aggregate:water-cement ratio). Fresh concrete properties, compressive, split tensile strengths, and modulus of rupture were measured for concrete mixtures with MCA within the investigated replacement levels. The results showed that the setting times of MCA concrete increased with higher ash content, while the compressive, split tensile strengths and modulus of rupture showed a reverse trend. It was further observed that almost all of the studied specimens attained over 70% of their 28-day strength at seven-day curing.