Mitigação da reação álcali-sílica em compósitos cimentícios com o uso de cinza volante e de escória granulada de alto forno do Complexo Industrial e Portuário do Pecém (Ceará)

Abstract

The alkali-silica reaction (ASR) in cementitious composites (mortars and concrete) is manifested by the chemical association of the matrix pores solution, which is strongly basic and rich in alkalis, and the reactive phases of certain aggregates. In order for the process to start, high relative humidity and a high concentration of total alkalis are required. ASR is one of the most common forms of alkali-aggregate reaction (AAR) in the world. The degradation resulting from this reaction involves expansion, cracking, exudation and decreased mechanical performance of the structure. In Brazil, the most advanced studies started after the building collapse in the city of Recife (PE), in 2004, culminating in the loss of human lives. Although AAR was not the main cause of the collapse, it aggravated the problem and served as a warning to professionals. Building foundation blocks have already been identified in Fortaleza (CE) with the occurrence of this reaction. Some studies have shown that the use of mineral additions, also called supplementary cementitious materials (SCM), can reduce or eliminate this pathological manifestation. Therefore, the study aimed at incorporating regional SCM, such as fly ash and granulated blast furnace slag from the Pecém Industrial and Port Complex, Ceará, in cementitious composites to assess the ASR mitigation capacity considering the incorporation of SCM during the cementitious composites production and during the manufacture of various types of Portland cements. The physical, chemical, mineralogical and microstructural properties of the SCM and the potentially reactive fine aggregate were analyzed. Mortar bars were produced to assess the ASR mitigation rate by the accelerated method and to identify the formation of possible reaction gels, cracks and warps. Chemical, mineralogical and microstructural tests were carried out on hardened mortars samples containing possible gels from ASR. Additionally, a statistical analysis was carried out to identify the influence of the CaO/SiO2 ratio and alumina on the expansion mitigation rate. The incorporation of SCM occurred as a partial replacement to standard cement in the percentages of 15%, 30% and 50% for fly ash and 35%, 45% and 55% for granulated blast furnace slag. Different types of Portland cements that contain such SCM in their compositions, from different manufacturers, available in the micro region of Fortaleza, Ceará, were also analyzed: CP II-Z-32-RS, CP II-E-32-RS, CP III-40 -RS and CP IV-32-RS. The results indicated a positive evaluation in the ASR development mitigation by the use of regional SCM, considering the incorporation during the commercial cement manufacture or during the mortars production. Considering that the production of these industrial by-products exceeds the flow currently given and that there is a concern of the technical environment with the seriousness of this pathological manifestation, such results are good indicators of alternative use in the civil construction chain of Fortaleza, Ceará.