Service life extension of concrete subjected to adverse curing conditions using internal curing meth

Abstract

Proper curing of concrete at early ages is crucial to obtain design strength and maximum durability. However, absence of proper curing is often observed specially in small to medium scale projects at remote locations due to lack of knowledge and awareness among the workers. Such improper curing results in weaker and permeable concrete and eventually, reduces the service life of RC structures significantly, particularly in aggressive environmental conditions. The primary cause for reduced service life is chloride induced corrosion resulting from ingress of chloride ion. The negative impacts caused by the lack of proper curing can be compensated by adapting the internal curing(IC) mechanism. In IC, additional water is supplied into the concrete from the internal source. In some recent studies, it is found that saturated brick chips (BC) can be used as internal curing (IC) medium within concrete. Brick chip has the ability to absorb sufficient quantity of water during mixing and desorbs it afterwards under favorable condition. Recent research shows that optimum proportion (20 percent replacement of stone chips by saturated BC) of BC as IC agent produce more durable concrete compared to the conventional concrete with 100 percent stone chips in the absence of proper curing. On the other hand, chloride ingress within concrete primarily depends on chloride diffusion coefficient of the concrete. Chloride diffusion coefficient is defined by the resistance to chloride penetration of particular concrete mix which can be evaluated by non-steady state migration test. As a result, concrete, mixed with optimum proportion of brick chip as IC agent is expected to linger the time of chloride corrosion initiation and its progress and eventually extend the service life of RC structure. In this context, a research effort has been undertaken to predict and extend the service life of RC structures with brick chips as IC medium under different simulated adverse curing condition. A total of 15 adverse curing conditions have been simulated in this study along with typical normal curing (CS) condition. For comparison, control samples (NC) with conventional stone chips were also made and subjected to normal and adverse curing conditions. It is observed that IC samples yielded lower diffusion coefficient values than that of NC samples under each adverse curing condition and subsequently produced concrete with higher corrosion initiation time. Besides, IC samples under comparatively extreme adverse curing conditions showed relatively better results than that of control samples (NC). Such trend was observed for all exposure classes with varying water cement ratios. Besides, higher values of concrete cover linger the corrosion initiation time by dawdling down the chloride ingress irrespective of curing condition. Finally, service life is predicted through combination of corrosion initiation time and time to sever cracking. In all cases of adverse curing conditions, internal curing exhibited enhanced service life as compared to normal samples. For example, internal curing can linger the service life by 4-16 for concrete under extreme exposure condition for a constant cover of 125mm. Similar results have been observed for other conditions also. Moreover, it has been observed that internal curing could achieve a particular target life expectancy against corrosion initiation time and eventually, a target service life under several adverse curing conditions whereas NC samples fail to do so.