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 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.

This study examines the impact of deicers on the compressivestrength and microstructure of concrete at ambient temperaturein sub-zero areas. In this study, after 7 days of curing in plainwater, concrete specimens were exposed to four deicer chemicalsolutions—sodium chloride, sodium acetate, calcium nitrate, andurea—at 3, 6, and 9% concentrations. The specimens were testedfor compressive strength after 14, 28, and 90 days of exposure. Alltested deicers, except calcium nitrate, have a propensity to decreasethe compressive strength of concrete. Exposure to sodium acetate,which appears to have the most detrimental effect, decreased thecompressive strength of concrete by a maximum of 30.79% at aconcentration of 9%, whereas exposure to calcium nitrate increasedthe compressive strength of concrete by 17% at a concentration of3%. Deicers changed the microstructure of concrete, which wasinvestigated using field-emission scanning electron microscopy(FE-SEM). 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 sub-zero environments, which were 10 to 11 days and 8.8% to 9%, respectively.

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

In this paper, several hundred specimens were compacted and tested to evaluate the potential of beam testing protocols to directly measure four mechanical properties from one beam. Mechanical properties measured through beam testing protocols were compared to properties of plastic mold (PM) device specimens and were found to be comparable once specimen densities were corrected. Mechanical properties were also used to quantify mechanical property relationships, often used as pavement design inputs. When compared to traditionally recommended mechanical property relationships, relationships between elastic modulus and unconfined compressive strength, as well as modulus of rupture and unconfined compressive strength, were overly conservative; however, indirect tensile strength and unconfined compressive strength relationships from the literature were accurate. This paper also assessed an elevated-temperature curing protocol to simulate later-life pavement mechanical properties on laboratory specimens. Mechanical properties of laboratory specimens that underwent accelerated curing were shown to be comparable to 10- to 54-year-old cores taken from Mississippi highways.

Reinforcing seawater sea-sand concrete (SSC) with basalt fiber reinforced polymer (BFRP) bars can adequately resolve chloride corrosion issues. However, the multiple-element ions in seawater and sea sand can increase the concrete alkalinity and accelerate the degradation of BFRP bars. This study aims to enhance the durability performance of BFRP-SSC beams by regulating concrete alkalinity. A low-alkalinity SSC (L-SSC) is designed by incorporating a high-volume content of fly ash and silica fume. A total of 16 BFRP-SSC beams were designed based on the current standards and prepared using normal SSC (N-SSC) and L-SSC. The beam flexural performances before and after long-term exposure are characterized through the four-point bending test. The test results indicate that exposure in the simulated marine environment can reduce the load-bearing capacity and change the failure mode of BFRP beams with N-SSC. After exposure at 55°C for 4 months, the load-bearing capacity of the BFRP-SSC beams was reduced by 70.0%. Moreover, a slight enhancement of load-bearing capacity and ductility of the BFRP-L-SSC beams was observed due to the enhanced interface performance with further concrete curing. Furthermore, the long-term performance of the sand-coated BFRP bars is better than that of the BFRP bars with deep thread. The load-bearing capacity of the BFRP-L-SSC beams increased by approximately 20% after 4 months of accelerated aging due to concrete strength growth, and the BFRP-L-SSC beams maintained the concrete crushing failure mode after exposure. Finally, a loadbearing capacity calculation model for the BFRP-SSC beams is proposed based on the experimental investigation, and its prediction accuracy is higher than that of the current standards. This study can serve as a valuable reference for applying BFRP-SSC structures in the marine environment.