Concrete Products

MAR 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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50 • March 2019 of each other," they say. "Therefore, a new curing membrane protocol is needed to eval- uate the quality of curing under a range of the weather conditions (i.e., temperature, relative humidity and wind speed), as well as the curing compound quality within a single index representing the effectiveness of the curing process," that is, the effective- ness index. Throughout the years, they add, different methods have been suggested for determin- ing the water content of fresh and hardened concrete. Determining the DC of concrete is a non-destructive test that can show the water content of concrete in various stages. These indicators were determined by mea- suring different factors for a given curing compound, such as moisture loss, surface abrasion resistance, surface porosity, and drying shrinkage. The EI and DC measure- ments were utilized as non-destructive tests to assess curing quality. For this study, a wax- based curing compound was tested according to preset laboratory conditions at different application rates to evaluate their suitability for the curing method. "The DC is a material's physical character- istic, which demonstrates its ability to store electrical energy," Joshaghani, Bhardwaj, Zollinger and Mukhopadhyay write. "The DC of free water is 80.1 at 20°C, which is con- siderably higher in solids, such as aggregate, cement and hydration products, which have a DC around 3 to 8. Free water content alludes to capillary pores at early ages, so DC can reflect the number of capillary pores." And because there is a linear relationship between free water content and DC, and this method is excellent for determining water content in the fresh concrete mixture. The authors conclude: • Several considerations regarding the utility of the direct and indirect measures were addressed to emphasize how EI and DC can be employed to assess curing quality. • The relative humidity and temperature of the curing affected concrete surface for calculating EI were measured to evaluate the curing practices. Results indicated that the moisture loss, sorptivity, and shrinkage measurements had a good correlation with EI values. It means that specimens with a higher EI value are associated with lower moisture loss measurements. • The surface abrasion weight loss results were found to have a significant correlation with EI. The higher EI values were associated with lower abrasion weight loss that represented a concrete surface with high abrasion resistance caused by an appropriate curing practice. • Curing at any application rate under windy conditions resulted in greater amounts of moisture loss, shrinkage, interconnected voids and sorptivity. The EI was also found to be influenced by ambient wind conditions. • Thin section microscopy was used as an effec- tive and comprehensive method to directly observe the effect of curing compound on the bleeding channels. The quantitative analysis of voids and carbonation appears to correlate to curing practice and expected performance. • The change in DC showed that the change in free moisture content at the surface could serve as an indicator of the effectiveness of curing at different application rates under different conditions. • The EI was found to be sensitive to wind conditions as well as the quality of differ- ent curing practices. A higher EI is generally associated with a lower decreasing rate of DC measurements and a better moisture reten- tion capability of the curing practice. • Results showed good potential for using DC measurements to extend the assessment of the curing practices' effectiveness beyond the EI usage. Thus, the utility of using DC measurements to qualify curing practices was validated. RECYCLED, FOAMED GLASS AGGREGATE FOR CONCRETE Recycled, foamed glass aggregate may work in concrete mixtures for transportation infrastructure, due to its enhanced ductility, say Daniel Nicholas, Lehigh Valley Technical Associates, Northampton, Pa.; Travis Shoe- maker, Schnabel Engineering, West Chester, Pa.; and, David Mante, Ph.D., Lafayette Col- lege, Easton, Pa., in their paper, Recycled Foamed Glass Aggregate Concrete for Use in Infrastructure Applications: A Pilot Study. "Foamed glass aggregates (FGA) are ultra-lightweight aggregates manufactured by heating a mixture of crushed recycled glass and a foaming agent, forming a material similar to natural pumice," the authors write. "To date, the use of FGA within concrete has been largely limited to non-structural civil engineering applications." Therefore, the objective of this study was to evaluate the suitability of FGA concrete for potential use in applications such as rein- forced concrete bridge girders, deck slabs, or roadway barriers, with a particular emphasis on flexural behavior. In this study, an FGA concrete mixture (50 percent coarse aggregate replacement by volume) with fresh and hard- ened properties suitable for reinforced concrete structural application was developed, refined, and incorporated into a full-scale reinforced concrete beam. The flexural response of the FGA specimen was compared to a control specimen incorporating conventional concrete (0 percent coarse aggregate replacement by volume) by load testing. The foamed glass material utilized in this research effort is an ultra-lightweight, closed-cell FGA produced by a proprietary combination of recycled glass powder, dry Concrete maturity meter system; knob at upper left is solar radiation sensor. IMAGE: Joshaghani, Bhardwaj, Zollinger, and Mukhopadhyay TECHNICAL TALK BY TOM KUENNEN

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