Optimizing metakaolin and silica-fume in rc beams with/without strengthening

Although cement is considered one of the most common materials as a basic component in producing concrete, its manufacturing consumes high energy accompanied by high carbon dioxide emission. Many types of metakaolin and silica-fume are used as a partial cement substitute. Most of the previous researches were conducted on relatively small-scale specimens. In this research, two folds are targeted to investigate the optimum cement replacements then their influential co-effect with external strengthening techniques of RC beams with a total of twenty-two relatively larger specimens. In the first fold, the attempt is made to use such partial cement replacements to reduce embodied carbon emission and hence carbon capture storage costs. For this purpose, thirteen beams with two types of metakaolin MKA, MKB and silica-fume are considered as cement replacements by 8, 12, 15 and 20% by weight. Effects on strength parameters, flexural behavior and ductility are studied and in turn, the optimum cement replacement ratios are determined as such. In the second fold of this investigation, nine specimens with cement replacement by 15% SF and MKA with three different strengthening techniques are considered. External steel plate bonding with end fasteners, near-surface mounted steel rebars and CFRP strips with end U-shaped wrapping are examined. The effects of cement replacement of each case are determined for compressive and tensile strengths. Cracking patterns, failure mechanism, load–deflection besides load–strain relationships and ductility index are investigated for the beam specimens. The research indicated that SF and MK may be used as a cement replacement up to 20% without any adverse effect for environment friendly concrete. The type of MK influences the optimum cement replacement ratio for enhancing the compressive or flexural strength. Size effect is proven to an aspect of consideration for a standardization of the optimum SF or MK replacement for flexure. Unless brittle modes of failure are secured, CFRP strengthening provides the highest ductility with reasonable strength enhancement. Durability characteristics in aggressive environments need further studies that expound their long-term features.