Purpose The purpose of this paper is to verify the influence of superplasticizer and air entrainment admixtures (AEs) in the electrical resistivity of concrete. Design/methodology/approach Ten different types of concrete have been studied. Three levels of superplasticizer and air AEs have been used (0.20, 0.35 and 0.50 per cent). Concrete samples were cast and the electrical resistivity was monitored at the ages of 28, 63 and 91 days. Compressive strength and density tests have also been executed. Findings The superplasticizer admixture presented an optimal level of 0.35 per cent that significantly increased the electrical resistivity. The air AEs at the same dosage caused a considerable decrease in the electrical resistivity. The concrete with air AEs showed highest resistivity/MPa ratio. Research limitations/implications The results should be carefully extrapolated for other materials and admixtures. Practical implications The usage of chemicals admixture in concrete is extremely common nowadays. However, only a few authors have studied the impact of such materials on the concrete’s electrical resistivity. Since many other researchers have already correlated electrical resistivity with other concrete’s properties, such as strength, setting time and corrosion probability, it is important to better understand how superplasticizers and air-entraining agents, for instance, impact the resistivity. Originality/value The vast majority of studies only tested the resistivity of cement paste or mortar and usually for short period of time (up to 28 days), which seems not to be adequate since the cement reaction continues after that period. This paper fills this gap and studied the impact of admixture on concrete and for a period of 91 days.

This paper describes an application of the Analytic Hierarchy Process (AHP) to choose the best cement type and mixture for the production of high performance concrete. The decision process aimed at obtaining a concrete that would best meet the requirements of three hypothetical scenarios: (a) industrial concrete floors of a chemical plant, (b) structural elements of a thirty-floor building and (c) a massive foundation block of a green building. In this regard, six different concrete mixtures were evaluated (VR4, IIIR4, V280, III280, V200 and III210) according to four criteria: mechanical properties, durability, financial cost and environmental impact. The analysis results showed that the composition with CPV-ARI cement and content of 280 kg/m3 was the best alternative for scenario (a) and (b), while for scenario (c) the composition with cement CPIII and content of 210 kg/m3 was the best choice.

PurposeEfflorescence formation is very common in cement-based materials. In the case of mortar, efflorescence is more studied when only Portland cement is used as a binder. However, the repair of historical heritage, as well as the construction system of some countries, usually uses mortars composed of hydrated lime and Portland cement. This study aims to determine the influence of the hydrated lime content on the incidence of efflorescence in mortars.Design/methodology/approachMortars with 0%, 50%, and 100% lime/cement ratio were studied, using three different methods to accelerate efflorescence formation. The surface area of mortars affected by efflorescence was quantified by analysis using image software. Also, analysis of mercury intrusion porosity test, flexural tensile, compressive strength, absorption of water by capillarity, porosity, XRD and TGA was performed.FindingsMore efflorescence in mortars with a higher amount of lime in their composition was observed. The results show that the increase in the lime content reduces the flexural tensile and the compressive strength and increased the absorption of water by capillarity and the porosity of the mortars. The material formed by the efflorescence was calcium carbonate, proven by microstructural tests.Originality/valueThe results of greater efflorescence formation in mortars with lime are important to alert users who apply this type of material. Some type of protection must be done more rigorously for lime-cement mortars, especially concerning contact with water, since efflorescence tends to be faster for this type of material.

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O objetivo desse estudo foi analisar o comportamento biomecânico de um cimento resinoso à compressão por meio do ensaio mecânico e do Método dos Elementos Finitos.Foram selecionados 20 pré-molares inferiores que foram submetidos à endodontia e à cimentação de pinos de fibra de vidro. Em seguida, as raízes foram seccionadas transversalmente, obtendo-se três discos de 3 mm de espessura. Os discos foram moldados e confeccionadas réplicas de resina epóxi, e os mesmos submetidos ao ensaio de compressão em uma máquina Shimadzu AG-I à velocidade de 1 mm/min e carga de 220 N.Após o ensaio mecânico, os discos foram novamente moldados e confeccionadas réplicas de resina epóxi. As réplicas foram observadas em microscopia eletrônica de varredura, onde foi selecionada uma imagem de um disco e transferida para o programa Auto-CAD 2007 para realização do modelo plano. Posteriormente, foi confeccionado o modelo tri-dimensional no programa ANSYS e simulado o mesmo ensaio. Os resultados sugeriram que o modelo computacional de adesão total apresentou uma distribuição de tensões adequadas, porém no corpo-de-prova real foi observada a presença de fendas previamente ao ensaio mecânico, o que dificultou a obtenção de adesão perfeita. Concluiu-se que a formação de fendas influenciou no comportamento do cimento.