International Concrete Abstracts Portal

The role of limestone (LS) powder replacement and changes in C-S-H due to pozzolanic reactions on the acid resistance of cementitious pastes are studied using thermodynamic modeling. Simulations are performed under equilibrium conditions while hydration products were exposed to increasing levels of sulfuric acid. LS replacement doesn’t show sacrificial characteristics against sulfuric acid attack, and LS acidification starts only after full consumption of portlandite, and most C-S-H. Increased LS replacement causes the dilution of the formed portlandite and C-S-H volumes, which results in their full consumption at lower acid concentrations than mixtures without LS replacement. Pozzolanic reactions of SCMs result in C-S-H phases with lower Ca/Si than OPC-only counterparts, increasing acid resistance. However, highly reactive and/or high-volume SCM replacements might further decrease the available portlandite, reducing the buffer acid resistance capacity. This issue is particularly critical for portland limestone cement-based systems.

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.

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.

In marine structures, concrete requires adequate resistance against chloride-ion penetration. As a result, numerous studies have been conducted to enhance the mechanical properties and durability of concrete by incorporating various pozzolans. This research investigated the curing conditions of samples including zeolite and metakaolin mixed with micro-/nanobubble water in artificial seawater and standard conditions. The results indicated that incorporating zeolite and metakaolin mixed with micro-/nanobubble water, cured in artificial seawater conditions, compared to similar samples that were cured in standard conditions, improved the mechanical properties and durability of concrete samples. The 28-day compressive strength of the concrete samples containing 10% metakaolin mixed with 100% micro-/nanobubble water and 10% zeolite blended with 100% micro-/nanobubble water cured in seawater increased by 25.06% and 20.9%, respectively, compared to the control sample cured in standard conditions. The most significant results were obtained with a compound of 10% metakaolin and 10% zeolite with 100% micro-/nanobubble water cured in seawater (MK10Z10NB100CS), which significantly increased the compressive, tensile, and flexural strengths by 11.13, 14, and 9.1%, respectively, compared with the MK10Z10NB100 sample cured in standard conditions. Furthermore, it considerably decreased the 24-hour water absorption and chloride penetration at 90 days— by 27.70 and 82.89%, respectively—compared with the control sample cured in standard conditions.

As the number of potential supplementary cementitious materials (SCMs) increase, there is a need to determine their reactivity. Most recent methods to assess pozzolanic reactivity are based on measuring certain outputs such as heat release (Q), calcium hydroxide (CH) consumption, and nonevaporable water. This paper uses thermodynamic modeling to aid in the interpretation of these tests and the quantification of reactivity. It is shown that pozzolanic reactivity should be interpreted based on the SCM type. The presence of sulfates and carbonates during reactivity quantification alter the reaction of the Al2O3 phases, making the interpretation of the reactivity test results challenging. The reactivity of commercial SCMs should be interpreted specific to the type of SCM as described by ASTM International/AASHTO. A proposed interpretation for commercial SCMs is provided in this paper.