Characteristics and Chloride Permeability of Internally Cured Concrete

This paper presents an experimental study on the physical characteristics of internally cured concrete using organic and inorganic materials, including chloride-related responses. The curing agents saturated before mixing the concrete are microporous lightweight aggregate (LWA), crushed returned concrete aggregate (CCA), and superabsorbent polymer (SAP). The inorganic agents (LWA and CCA) replace the concrete's fine aggregate by 25 to 75% in mass, while the organic agent (SAP) is added to the concrete mixture by 0.2 to 0.6% of the cement mass. A variety of test schemes are employed-namely, compression strength, resonant frequency, drying shrinkage, chloride permeability, and digital microscopy. Selected specimens are preloaded to examine the performance of the internally cured concrete subjected to service loading. The compressive strength of the concrete decreases as the amount of the curing agents increases. The strength decrease rate of the LWA- and SAP-mixed concrete is more rapid than that of the CCA-mixed concrete. In terms of resonant frequency, the LWA-mixed concrete is more susceptible relative to its CCA and SAP counterparts because of the LWA's microporous structure. The concrete mixed with LWA reveals dynamic to static elastic modulus ratios higher than the concrete with the other agents. Although all concrete mixtures' drying shrinkage is influenced by the agents' quantity, the inclusion of SAP results in more shrinkage. Electric charges passed through the internally cured concrete are higher than those of the control concrete, which represent the degree of chloride permeability. The occurrence of cracks in the concrete caused by preloading accelerates the mobility of chloride ions; nonetheless, the addition of SAP alleviates the implications of the mechanical damage.