This study examines the impact of deicers on the compressive strength and microstructure of concrete at ambient temperature in sub-zero areas. In this study, after seven days of curing in plain water, concrete specimens were exposed to four deicer chemical solutions: sodium chloride, sodium acetate, calcium nitrate, and urea at 3%, 6%, and 9% concentrations, respectively. The specimens were tested for compressive strength after 14 days, 28 days, and 90 days of exposure. All tested deicers, except calcium nitrate, have a propensity to decrease the compressive strength of concrete. Exposure to sodium acetate, which appears to have the most detrimental effect, decreased the compressive strength of concrete by a maximum of 30.79% at a concentration of 9%, whereas exposure to calcium nitrate increased the compressive strength of concrete by 17% at a concentration of 3%. Deicers changed the microstructure of concrete, which was investigated using Field Emission Scanning Electron Microscopy (FESEM). This was followed by X-ray diffraction (XRD) for qualitative analysis of phases present in deicer-treated concrete specimens. The desirability function was used to determine the optimal exposure period and calcium nitrate concentration for concrete in subzero environments, which were respectively 10 to 11 days and 8.8 to 9%.

Lightweight concrete (LWC) finds wide-ranging applications in the construction industry due to its reduced dead load, good fire resistance, and low thermal and acoustic conductivity. Lightweight geopolymer concrete (LWGC) is an emerging type of concrete that is garnering attention in the construction industry for its sustainable and eco-friendly properties. LWGC is produced by using geopolymer binders instead of cement, thereby reducing the carbon footprint associated with conventional concrete production. However, the absence of standard codes for geopolymer concrete restricts its widespread application. To address this limitation, an investigation focused on developing a new mixture design for LWGC by modifying the existing ACI 211.2-98 provisions has been carried out. In this study, crucial parameters of LWGC such as alkaline/binder ratio, molarity, silicate/hydroxide ratio, and curing temperature were established using machine learning techniques. As a result, a simple and efficient method for determining the mix proportions for LWGC has been proposed.

Determining the in-place properties of mass concrete placements is elusive, and currently there are minimal to no test methods available that are both predictive and a direct measurement of mechanical properties. This paper presents a three-stage testing framework that uses common laboratory equipment and laboratory scale specimens to quantify thermal and mechanical properties of mass high-strength concrete placements. To evaluate this framework, four mass placements of varying sizes and insulations were cast, and temperature histories were measured at several locations within each placement, where maximum temperatures of 107 to 119°C (225 to 246°F) were recorded. The laboratory curing protocols were then developed using this mass placement temperature data and the three-stage testing framework to cure laboratory specimens to represent each mass placement. Laboratory curing protocols developed for center and intermediate regions of the mass placements reasonably replicated thermal histories of the mass placements, while the first stage of the three-stage framework reasonably replicated temperatures near the edge of the mass placements. Additionally, there were statistically significant relationships detected between calibration variables used to develop laboratory curing protocols and measured compressive strength. Overall, the proposed three-stage testing framework is a measurable step toward creating a predictive laboratory curing protocol by accounting for the mixture characteristics of thermomechanical properties of high-strength concretes.

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.

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.