Activated alkali cements: effect of thermal curing on the development of mechanical strength

摘要

Due to the extraction of nonrenewable raw materials and the release of CO2 into the atmosphere by the production of Portland cement, the alkali-activated cements (AAC) have been gaining ground in the world scenario since their production process does not involve calcination of the raw materials and uses various byproducts. Thus, they are considered as a low environmental impact product and with good engineering properties. The AAC's can be obtained mainly from blast furnace slag (BFS), which may have origin in charcoal ovens or coke, which modifies their chemical composition. The objective of this work was to evaluate the influence of the chemical composition of BFS on the behavior of the AAC and to investigate the thermal cure efficiency in the improvement of the compressive strength. For the production of AAC, two slag, A and B, were used from charcoal kilns and coke, respectively, in addition to sodium hydroxide as an alkaline activator. The samples were subjected to thermal cure for a period of 24 hours at temperatures of 40 oC and 60o C, which were subjected to the compressive strength, calorimetry and microstructure analyzes at 3, 7 and 28 days. The results showed that slag A was more reactive and more influenced by the cure temperature. The AAC made with BFS- A (AAC / A) slag presented higher mechanical performance than B (AAC / B) at at all temperatures. Microstructure analyzes showed that in AAC/A there was a majority formation of CSH, while in CAT/B, CSH and hydrotalcite. Thermal curing was not efficient to improve the mechanical behavior of CAT / B.