Influence of curing on the properties of concretes and mortars in hot climates
This investigation deals with the influence of initial curing periods and different curing environments, similar to those found in Middle Eastern countries, on the pore size distribution, permeability, water absorption and compressive strength of cement mortars and concretes made with and without pulverized fuel ash (pfa) and ground granulated blast-furnace slag (ggbs). Three 00 environments were chosen as follows: 1) 20C+70%RH, 2) 35C+70%RH, and 3) 45C+30%RH. To simulate in-place casting, the initial mix temperatures were controlled to be as close as possible to that of the environment in which the mixes were to be kept and moisture loss was allowed to occur from only the top-as-cast face of the specimen. Durability of the mortar specimens was assessed using pore size distribution, oxygen permeability, air permeability and water absorption. In addition to strength, the following tests were carried out on the concrete specimens to assess durability: initial surface absorption (ISAT), water absorption,relative air permeability and porosity. An the tests carried out on all specimens were undertaken at an age of 28 days. 7be test results showed that the durability properties of all specimens were significantly improved as curing periods increased. While curing durations had some significant effect on the strength of OPC/ggbs samples, the effects on OPC and OPC/pfa were in general only minimal. Furthermore, as to the effects on the pore size distribution and permeability, a critical curing duration (beyond which no further significant changes in these properties were observed) was seen to exist which depended on both curing environment and cement type. Enviromnents hotter than 20C+70%RH adversely affected the durability properties of uncured samples of all mixes. Furthermore, the durability properties of plain OPC samples were adversely affected by the two hot environments when compared to 20C+70%RH for all curing durations. On the other hand, while OPC/pfa and OPC/ggbs samples cured for one day or more at 35C+70%RH showed similar or worse durability results compared with those cured at 20C+ 70%RH, better results were obtained at 45C+30%RH than in either of the other two environments. As to the effects on strength, for any given curing period, environments hotter than 20C +70%RH adversely affected the OPC and OPC/ggbs samples but not those containing pfa. AT 20C+70%RH,the pfa specimens showed generally similar or worse durability results and weaker samples than plain OPC for all curing periods. This trend was reversed in the two hot environments. On the other hand, while OPC/ggbs samples showed similar or worse durability results at 20C+70%RH and 35OC+70%RH compared to plain OPC, at 450C+30%RH the slag specimens showed better durability results for curing periods of one day or more. Tbe 28-day strength of OPC and OPC/ggbs concretes were similar to each other in all envimnments for all curing periods except for those which were uncured. The uncured OPC specimens were stronger than the slag specimens in all envimnments.