International Concrete Abstracts Portal

In the last four decades, numerous investigations have been undertaken on abrasion-erosion of concrete using various test methods. These have suggested the existence of different abrasion mechanisms, limitations of existing test methods, and inconsistencies on the importance of compressive strength to abrasion resistance of concrete. The objective of this review is to understand the mechanisms of concrete abrasion-erosion, assess the suitability of existing test methods to simulate field conditions, and investigate the relationship between abrasion resistance and compressive strength. It is found that concrete abrasion mechanisms are dependent on both transport modes of abrasive charge and the ratio of coarse aggregate to matrix hardness. The ASTM C1138 (underwater) test method appears to simulate all the critical modes of sediment-induced abrasion expected in field conditions and specific energy can be used as a framework to correlate ASTM C1138 test results with field measurements. With the exception of concrete with rubber aggregates, abrasion loss is found to fit a simple power function of its compressive strength, and no significant improvements in abrasion resistance can be gained by using concretes with compressive strengths exceeding 60 MPa (8.70 ksi). Also, the influence of cementitious additives and coarse aggregate properties is only significant at compressive strengths below the optimal value of 60 MPa (8.70 ksi).

A comprehensive research project was undertaken to evaluate the effect of styrene butadiene rubber (SBR) latex admixture on washout loss and bond strength of underwater concrete (UWC) designated for repair applications. Three UWC series possessing low to high stability levels that incorporate 5 to 15% SBR, by binder mass, were tested. A 1.5 m (4.93 ft) long specially designed channel was developed to enable the UWC to free fall from the outlet of a V-funnel apparatus, flow along an inclined surface submerged in water, then spread onto a horizontal concrete surface. Results show that underwater casting leads to reduced pulloff strengths caused by washout loss and aggregate segregation that weaken in-place properties. The incorporation of SBR was particularly efficient to reduce washout loss and improve adhesion between the repair overlay and substrate. Regression models enabling the prediction of residual bond strengths from the UWC rheological properties, washout loss, and polymer content are established.

Correlations between compressive strength and electrical resistivity of concretes exposed to different aggressive conditions were sought to evaluate concrete quality. Concrete specimens were cast with four water-cement ratios (w/c) and exposed to five different conditions of water, chloride, and sulfate solutions. Electrical resistivity and compressive strength tests were performed from 28 to 189 days. The results were statistically analyzed and supported by SEM and XRD analyses. When correlating both properties, higher coefficients of determination were found for conditions of underwater and wetting and drying cycles in water. In general, 71.4% of the coefficients of determination were greater than 0.700. The lowest correlations were found for concrete exposed to chloride solutions because the electrical resistivity of the specimens in these conditions tends to remain constant over time.

A comprehensive research project was undertaken to evaluate the effect of hydrostatic pressure and interfacial concrete/water velocity on the performance of underwater concrete (UWC) designated for repair applications. Washout loss was determined on 33 optimized mixtures using the CRD C61 test method, as well as a newly developed device enabling the simulation of concrete washout placed at various depths down to 140 m (460 ft) below water surface level. Test results showed that washout loss of UWC increases with the increase in water head. Depending on the mixture composition, a critical threshold water depth can be found, beyond which significant washout loss could take place. The effect of decreasing the interfacial concrete/water velocity from 2.5 to 0.5 m/s (8.2 to 1.6 ft/s) was found to reduce washout loss for a given depth of casting or enable the casting in deeper water for a given washout resistance. Good correlations were obtained between washout loss determined as per the CRD C61 test method and the washout loss derived from estimates given a certain interfacial concrete/water velocity and water depth.

Antiwashout admixtures (AWAs) are mostly organic polymers incorporated into concrete intended for underwater placement and repair to reduce the risk of water dilution and separation of solid constituents. Such polymers are also used for highly workable concrete proportioned to flow under its own weight and self-compact with minimum segregation. This paper investigates the effect of two commonly used AWAs on washout resistance and rheology of highly flowable concrete. Test results show that for mixtures with fixed slump consistency, the incorporation of an AWA can greatly reduce water dilution and increase flow resistance and plastic viscosity of the concrete. These results are more accentuated at relatively high concentrations of AWA. Slump consistency cannot reflect the degree of washout resistance of AWA concrete. Washout resistance, however, is found to vary with the rheological parameters of the concrete calculated from the Bingham model. Rheological workability zones are defined for flow resistance and torque plastic viscosity combinations that can correspond to various levels of washout resistance. The V-funnel flow time test is shown to correlate well to plastic viscosity of highly flowable underwater concrete and, hence, can be useful to assess the impact of AWA on washout resistance in the field.