International Concrete Abstracts Portal

Reinforced concrete (RC) members undergoing shrinkage are susceptible to cracking when restrained; however, studies on this behavior are limited. Thus, the main objective of this paper is to present crack-widths, crack-patterns, and shrinkage strains from an experimental study on three RC walls with aspect ratios of 3.26 and 1.08, and horizontal reinforcement ratios of 0.2% and 0.35%, as well as a rectangular tank with 0.24% reinforcement. A 3-D nonlinear finite element (FE) analysis is conducted, and the results reveal that although the model predicts strains and maximum crack-widths reasonably well, the crack-pattern differs from the experiments. The possible reasons for this difference are discussed, and a parametric study is done to propose design equations to estimate restraint factors along the wall centerline for different aspect ratios. These equations can be used to estimate the cracking potential in the design stage without the need for a nonlinear FE analysis. For L/h above four, horizontal reinforcement has a negligible effect on the restraint, and for L/h above eight, full-height cracks can be expected due to almost uniform restraint. Finally, the design codes are compared, and it is found that ACI 207.2R-07 and CIRIA C766 predict shrinkage-induced crack-widths conservatively and reasonably accurately.

Crack densities obtained from on-site surveys of 74 bridge deck placements containing concrete mixtures with paste contents between 22.8% and 29.4% are evaluated. Twenty of the placements were constructed with a crack-reducing technology (shrinkage-reducing admixtures, internal curing, or fiber reinforcement) and 54 without; three of the decks with fiber reinforcement and nine of the decks without crack-reducing technologies involved poor construction practices. The results indicate that using a concrete mixture with a low paste content is the most effective way to reduce bridge deck cracking. Bridge decks with paste contents exceeding 27.3% had a significantly higher crack density than decks with lower paste contents. Crack-reducing technologies can play a role in reducing cracking in bridge decks, but they must be used in conjunction with a low paste content concrete and good construction practices to achieve minimal cracking in a deck. Failure to follow proper procedures to consolidate, finish, or cure concrete will result in bridge decks that exhibit increased cracking, even when low paste contents are used.

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 their 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, along with two other types of ICMs, on various properties of high-performance concrete in the hardened state under two curing conditions. Concrete mixtures were prepared with pre-wetted RAs, superabsorbent polymers (SAPs), and pre-wetted lightweight volcanic aggregates (LWVAs) as ICMs. Concrete performance was compared through the investigation of 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 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 mixtures 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.