The conventional external curing process requires supply of large amount of water in addition to mixing water as well as strict quality control protocol. However, in a developing country like Bangladesh, many local contractors do not have awareness and required knowledge on importance of curing which often results in weaker concrete with durability issues. Moreover, at times it is difficult to maintain proper external curing process due to nonavailability of water and skilled laborer. Internal curing can be adopted under such scenario since this method is simple and less quality intensive. Usually, naturally occurring porous light weight aggregates (LWA) are used as internal curing agent. However, naturally occurring LWA are not available in many countries like Bangladesh. Under these circumstances, Super Absorbent Polymer (SAP) can be utilized as an alternative internal curing agent. In this study, sodium polyacrylate (SP) as SAP has been used to produce internally cured concrete. Desorption isotherm of SP has been developed to investigate its effectiveness as internal curing agent. Test results showed that internally cured concrete with SP performed better in terms of both strength and durability as compared to control samples when subjected to adverse curing conditions where supply of additional water for external curing was absent.
Proper curing of concrete is essential for achieving desirable mechanical properties. However, in a developing country like Bangladesh, curing is often neglected due to lack of proper knowledge and skill of local contractors. Consequently, general concreting work of the country has been found to have both strength and durability issues. Under such scenario, internal curing could be adopted using masonry chip aggregate (MCA) which is quite common in this region. It is observed that saturated MCA desorbs water under favorable relative humidity and temperature. This paper presents the effectiveness of MCA as internal curing medium and recommends a tentative optimum mix proportion to produce such concrete. The experimental study was conducted in two phases. It was found that 20% replacement of stone chips with MCA produced better performing internally cured concrete both in terms of strength and durability. Performance of internally cured concrete with recommended proportion of MCA is comparable to that of normally cured control concrete samples with conventional stone chips. In addition, internally cured concrete performed significantly better than control samples when kept under similar adverse curing conditions. In the absence of supply of external water for curing, compressive strength of internally cured concrete for 20% replacement can be as high as 1.5 times the strength of the control concrete samples. Significant better performance in permeability than that of control samples was also observed for this percent replacement under such adverse curing conditions. Keywords: internal curing, lightweight aggregate, temperature, humidity, desorption, strength, permeability. Abbreviations IC
Durability means the resistance to physical or chemical deterioration of concrete resulting from interaction with environment (physical deterioration) or interaction between constituents (chemical deterioration) of concrete. A durable concrete ensures corrosion resistance of embedded steel which in turn ensures a better longevity of the structure as a whole. Concrete in structures in the coastal areas are the most susceptible to chemical deterioration as sea water, with high concentration of chloride ions, has quite a detrimental effect on durability of concrete. In these cases, the lower the chloride permeability, the better the durability of concrete. As instruments for standard chloride permeability test is very expensive, an experiment has been conducted to carry out Rapid Chloride Permeability Test (RCPT) using improvised apparatus made of readily available low-cost materials. Several RCPT tests were performed using this simple method and results showed marked variation in chloride permeability for concrete with different quality.
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