The dimensioning of structural systems in reinforced or prestressed concrete requires knowledge, among other properties, at least of the deformation modulus and compressive strength. However, concrete may present enough strength, whereas the structure rigidity might not be compatible with minimum required values for the verification of possible deformations. In Brazil, the estimate of deformation modulus is made using the NBR 6118 theoretical equation and internationally, the main theoretical models used are recommended in ACI 318, Eurocode 2, and the fib Model Code. But the bibliography indicates that there is no confidence in the models proposed. The present study aims to analyze the isolated effect of paste volume on the portland cement concrete deformation modulus. The results of the study indicate a significant influence of paste volume on the module value and, because a reduction in the amount of paste volume occurs, the concrete deformation modulus increases for all ages. The lack of consistency is also observed between experimental values and those obtained by theoretical equations, suggesting independency of the two magnitudes, compressive strength, and deformation modulus.

The paper presents an experimental investigation on durability performance of colloidal nanosilica-added high-volume fly ash concrete (HVFAC) mixtures made with coarser unprocessed siliceous fly ash (with its proportion varying from 50 to 70% in the cementitious matrix) under chloride exposure. Chloride-induced corrosion is a serious durability concern for reinforced and prestressed concrete structures, and corrosion of reinforcement severely lowers the service life of structures. Therefore, an attempt has been made in this study to investigate, through rapid chloride permeability and chloride penetration tests, the performance of HVFAC mixtures under chloride ingress by migration and diffusion mechanisms. The permeability test results have been further corroborated with electrical resistivity of these concretes. The corrosion behavior of reinforcing bar embedded in test specimens made with these concretes was also investigated. The study indicated that the addition of small quantities of colloidal nanosilica significantly improved the resistance to chloride ingress and increased resistance to the corrosion of reinforcing bar in HVFAC.

Carbonation curing has demonstrated potential of improving concrete performance while facilitating carbon dioxide utilization. However, reinforcement corrosion behavior in carbonation-cured concrete has not been documented. This paper presents a study on chloride-induced corrosion in reinforced concrete subjected to carbonation curing. A special carbonation curing process was developed for precast non-prestressed applications. Performance of carbonation curing was evaluated by concrete compressive strength, pH value, and carbon dioxide uptake, while corrosion resistance of the carbonation-cured concrete was assessed by reinforcing bar mass loss and concrete chloride content. To understand the mechanism, concrete and cement paste were further characterized using mercury intrusion porosimetry, absorption, and electrical resistivity tests. Micromorphology was assessed by scanning electron microscopy. It was found that apart from rapid early-age strength gain, carbonation curing could significantly reduce chloride permeation in concrete concerning both total and free chloride contents. It was attributed to the reduced pore size and pore volume by calcium carbonate precipitation. With subsequent 28-day hydration, the carbonation-cured concrete displayed a pH over 12.0 at the surface of steel reinforcing bars and a micromorphology similar to the non-carbonated reference. The direct corrosion tests showed that the corrosion-induced mass loss of steel reinforcing bar was lessened by 50% in concrete subjected to carbonation curing.

There is still a concern regarding concrete structures’ fire safety, mostly due to the occurrence of concrete spalling. Although many tests have already been carried out, there is no clear definition about the parameters of the factors that influence its occurrence. This paper aimed to compare three different types of concrete panels, with dimensions of 300 x 315 x 10 cm (124.0 x 39.4 x 3.9 in.), composed of reinforced concrete (RC), prestressed concrete, and polypropylene microfiber RC. The panels were exposed to the standard fire curve based on ISO 834, aged 28 days, measuring the temperatures in panels’ surfaces. Prestressed concrete panels experienced explosive spalling 18 minutes after the test began. RC panels and the panels with polypropylene microfiber addition maintained their integrity and structural stability for 240 minutes, failing in the thermal insulation criteria at 210 and 140 minutes, respectively. Although polypropylene microfiber concrete panels presented no spalling of concrete, conventional concrete panels attended the standardized criteria for a longer period due to its better thermal insulation.

Estimating the time-dependent behavior of self-consolidating concrete (SCC) is essential for its successful use in prestressed concrete applications. Compliance is the total load-induced strain (elastic and creep strain) at any age per unit stress caused by a sustained applied load. Compliance of SCC is compared to that of conventional-slump concrete (CSC). Four SCC and one CSC mixtures were made under controlled laboratory conditions and tested under sustained load applied at either 18 hours, 2 days, 7 days, 28 days, or 90 days. All SCC mixtures cured under elevated or standard laboratory temperatures exhibited compliance values less than or similar to the CSC mixture. The accuracy of six compliance prediction methods was also investigated. The compliance prediction accuracy achieved for SCC is similar to that for CSC. The CEB 2010 model was the most accurate compliance prediction method regardless of concrete type or curing condition.