International Concrete Abstracts Portal

Compared to external curing, internal curing enables the judicious use of available water to provide additional moisture in concrete for more effective hydration, and improvement in the performance of concrete structures. However, certain challenges with the incorporation of internal curing materials (ICMs) still need to be addressed as its effectiveness depends on several factors. Furthermore, sustainable construction demands the use of recycled materials, and this paper discusses the comparative evaluation of recycled aggregate (RA) as an ICM with two other types of ICMs on various properties of high-performance concrete in the hardened state under two curing conditions. Concrete mixes were prepared with pre-wetted recycled aggregates (RA), superabsorbent polymers (SAPs), and pre-wetted lightweight volcanic aggregates (LWVA) as ICMs. Concrete performance was compared through the investigation on the strength development, shrinkage, mass loss, and volumetric water absorption. In addition, the change in internal humidity of concrete with time at different stages of hardening was determined. The compressive strength results showed that RA and LWVA are more efficient in the early days, and the performance of SAP is better in the later age due to its slow water-releasing capabilities. Compared to the control mixture, the least reduction in strength of 4% and 8% at 28 days and 90 days, respectively could be observed for the mixes containing RA under both air and water curing.

Ground-glass pozzolan has recently been considered a supplementary cementitious material by Canadian (CSA A3000) and American (ASTM C1866/C1866M) standards, but limited studies have been done on ground-glass use on-site. So, in this study, several sidewalk projects were performed by the SAQ Industrial Chair at the University of Sherbrooke from 2014 to 2017 on fields with different proportions of ground glass (that is, 10, 15, and 20%) in different conditions considered in such a cold climatic region. Sidewalks are a nonstructural plain concrete element that are among the most exposed to chloride and freezing and thawing in saturated conditions of municipal infrastructures. Coring campaigns were carried out on these concretes after several years of exposure (between 5 and 8 years). The results of core samples extracted from the sites were compared to the laboratory-cured samples taken during the casting. These laboratory concrete mixtures were tested for fresh, hardened (compressive strength), and durability (freezing and thawing, scaling resistance, chloride-ion penetrability, electrical resistivity, and drying shrinkage) properties (up to 1 year). The results show that ground-glass concrete performs very well at all cement replacements in all manners in terms of long-term performance. Besides that, using ground-glass pozzolan in field projects also decreases the carbon footprint and environmental and glass disposal problems.

Though extensive experimental studies have been conducted for shrinkage, studies focusing on shrinkage of high volume-to surface ratio (V/S) concrete in low-relative-humidity conditions are relatively scarce. Accordingly, most shrinkage prediction models are applicable for relatively medium- to high-humidity conditions with a V/S of 100 mm (3.9 in.) or less. In this study, to evaluate the prediction accuracy of current shrinkage prediction models for conditions with high V/S and low-relative-humidity conditions, long-term measurements of shrinkage were conducted with 28 rectangular prism-shaped concrete specimens 76.2 x 76.2 x 285 mm (3.0 x 3.0 x 11.2 in.) or 125 x 125 x 550 mm (4.9 x 4.9 x 21.7 in.) in size with V/S ranging from 16.8 to 285 mm (0.7 to 11.2 in.). The results reveal that current shrinkage prediction models, such as the ACI 209R-92, fib Model Code 2010 (MC2010), B3, and GL2000 models, can significantly underestimate the long-term shrinkage in relative humidity less than 20%, depending on the V/S. The prediction accuracy of the ACI 209R-92 and fib MC2010 models depends on how model parameters on the member’s geometry, such as the V/S, are determined.

This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 με and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC.

A comprehensive laboratory testing program, field-testing program, numerical analysis, and life-cycle cost analysis were conducted to evaluate the beneficial effects of incorporating shrinkage-reducing admixture (SRA), polymeric microfibers (PMFs), and optimized aggregate gradation (OAG) into internally cured concrete (ICC) mixtures for rigid pavement applications. Results from the laboratory program indicate that all the ICC mixtures outperformed the standard concrete (SC) mixture. All the ICC mixtures showed a decrease in drying shrinkage compared to the SC mixture. Based on the laboratory program, three ICC mixtures and one SC mixture were selected for the full-scale test and subjected to a heavy vehicle simulator for accelerated fatigue testing. Extensive testing and analysis have shown that ICC mixtures incorporating SRA, PMFs, and OAG can be beneficially used in pavement applications to achieve increased pavement life.