Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.

This paper compiles results from three different laboratory studies and employs multivariate regression analyses to model the effect of mixture parameters and concrete hardened properties on saltscaling performance. The correlations between concrete hardened properties and mixture proportions were also studied. The modeled mixture parameters included water-cementitious materials ratio (w/cm), slag cement, and air content. Concrete performance was evaluated through abrasion resistance, sorptivity, compressive strength, and salt scaling tests. According to the results obtained in this study, concrete scaling performance is affected, in the order of importance, by w/cm, slag-cement replacement, and air content. In addition, concrete hardened properties, especially abrasion resistance, were found useful in making reliable salt-scaling predictions. Based on the results derived from the regression analyses and the discussions provided in the reviewed literature, recommendations are given for proportioning of concrete to obtain adequate performance with respect to compressive strength, abrasion resistance, sorptivity, and salt-scaling resistance. In addition, the relationship between concrete properties, ingredients, and effective mechanisms are investigated.

The pore solution expressed from 28-day cement pastes was analyzed as part of a wider research program investigating the corrosion behavior of stainless-steel reinforcing bars in concrete, using inductively coupled plasma and ion chromatography techniques. The pastes were prepared with different water-cementitious materials (binder) ratios (w/cm), portland cement with and without supplementary cementitious materials (SCMs), and with admixed sodium chloride in the range typical of the threshold values for stainless steel reinforcement. The major anion and cation concentrations are given, showing the influence of admixed chloride on the amount of chloride retained in solution and of sulfate released into the pore solution. The results are discussed in terms of the initial compositions of the cementitious materials and their effect on chloride binding.

The main objective of this paper is the investigation of the corrosion resistance of reinforced concrete containing various proportions of recycled aggregates (RA) combined with 25% ground-granulated blast-furnace slag (GGBS) as a partial cement replacement. An accelerated corrosion system was designed to test the steel corrosion in reinforced concrete by subjecting the samples to 150 and 300 wetting-and-drying cycles. The results, in general, showed that the use of RA in concrete mixtures was found to reduce the compressive strength, increase chloride penetration, decrease the corrosion potential of reinforcing bars, reduce the electrical resistance of concrete, and hence increase the corrosion risk. However, better results were achieved by the addition of 25% GGBS, which increased the core compressive strength and electrical resistance. Moreover, better results were achieved for normal and slag mixtures that have 0.788 in. (20 mm) concrete cover than those having 0.394 in. (10 mm) cover.

The research presented in this paper addresses the effect of coarse recycled concrete aggregate (RCA) on drying shrinkage of concrete designated for transportation infrastructure. Six types of RCA were employed at 30 to 100% replacement rates of virgin coarse aggregate. Two binder systems, including a binary cement with 25% Class C fly ash and a ternary system with 35% fly ash and 15% slag were employed. Three different water-cementitious materials ratios (w/cm) of 0.37, 0.40, and 0.45 were considered. Test results indicate that the use of RCA increased drying shrinkage by up to 110% and 60% after 7 and 90 days of drying, respectively. Correlations with R2 of up to 0.85 were established to determine the shrinkage at 7, 28, 56, and 90 days as a function of aggregate properties, including specific gravity, water absorption, and Los Angeles abrasion resistance of the combined coarse aggregates. The water absorption of the combined coarse aggregate was shown to be a good index to showcase the effect of RCA on shrinkage. Contour graphs were developed to determine the effect of RCA content and its key physical properties on 90-day drying shrinkage of concrete intended for rigid pavement construction. A classification system available in the literature was also used to suggest the maximum allowable replacement rates for use of RCA in a hypothetical case study. Results suggest replacement rates of 100%, 70%, and 50% (% wt.) to limit the 90-day shrinkage to 500 μɛ when RCA of A-1, A-2, and A-3 Classes are available, respectively.