American Concrete Institute ACI Materials Journal January 2018
Physical Characteristics and Chloride Permeability of Internally Cured Concrete Studied Using Organic and Inorganic Materials
Authors: Yail J. Kim, Jun Wang, and Yongcheng Ji
Newswise — An experimental study examines 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) (Fig. 1). The inorganic agents (LWA and CCA) replaced the fine aggregate in the concrete by 25 to 75 percent in mass, while the organic agent (SAP) is added to the concrete mixture by 0.2 to 0.6 percent of the cement mass.
With an increase in the replacement ratio, the strength decrease rate of the LWA-mixed concrete was more rapid than the CCA-mixed concrete. According to the measured coefficients of variation, the LWA and CCA agents were speculated to be dispersed erratically inside the concrete. The SAP-mixed concrete showed a strength decrease rate similar to the LWA case with lower coefficients of variation.
The resonant frequency of the internally cured concrete decreased when the amount of agents increased. The LWA-mixed concrete’s frequency variation was not as sensitive to the quantity of agents as its CCA and SAP counterparts, primarily due to the microporous lighter weight of the LWA. The ratio between the dynamic and static elastic moduli of the LWA-mixed concrete was noticeably high (up to 1.67), whereas the ratio of the CCA- and SAP-mixed concrete was close to unity.
The concrete’s drying shrinkage was influenced by the amount of curing agents. The strain development of the SAP-mixed concrete was more pronounced than that of the LWA- and CCA-mixed concrete. Insignificant microcracks were observed in the internally cured concrete (Fig. 2). After preloading the concrete, wider cracks were noticed that were owing to mechanical damage.
The electric charge of the concrete mixed with the internal curing agents was greater than that of the control concrete. The charges rose until the concrete’s micropores were saturated by sodium chloride. The aforementioned preload-induced cracks facilitated chloride flows across the concrete, thereby increasing the quantity of chloride ions. In terms of chloride permeability, the concrete with the organic SAP agent was less sensitive to mechanical damage relative to the concrete with the other inorganic agents.
The research can be found in a paper titled “Characteristics and Chloride Permeability of Internally Cured Concrete,” published by ACI Materials Journal.
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