International Concrete Abstracts Portal

In this work, novel polycarboxylate admixtures were synthesized by two different free radical polymerization systems of methacrylic acid (MAA) and methoxy polyethylene glycol methacrylate (MPEG-MA) for PC-1, and acrylic acid (AA) and iso amyl alcohol polyethylene glycol (IAA-PEG) for PC-2. Thioglycolic acid as a chain transfer agent and ammonium persulphate as an initiator were used. The synthesized carboxylic polymers were characterized using FTIR, H-NMR, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). The influence of the chemical structure of polycarboxylates on the rheology of the concrete, as well as the prognosis of the superplasticizer’s development, is also presented through measuring water consistency, setting times, flow table, slump test, Zeta potential, and compressive strength. The cementitious products were investigated with X-ray diffraction (XRD) and scanning electron microscope (SEM). The developed superplasticizers have shown good dispersion effects and slump performance in workability and fluidity retention tests, adsorption performance, and scanning electron microscopy performance. Intriguingly, the PC-1 and PC-2 mixes achieved flow table values of 230 and 200 mm, respectively. The compressive strength values at various curing ages up to 28 days exhibited double and triple values compared with the control sample. Additionally, compared to the control ordinary Portland cement paste, a reduction of water-to-cement ratio of about 0.25 and the development of excessive hydration products give PC-1 and PC-2 extensive pastes a more dense and compact structure in XRD and SEM investigation.

To prepare the SiO2 aerogel gypsum-based lightweight thermal insulation wall materials with better water resistance, α-hemihydrate gypsum (HG) was used as the main cementitious material. By adding Portland cement (PC), fly ash (FA), and hydrated lime (HL), HG was modified. Using these materials, the HG-PC system and HG-PC-FA-HL system were constructed, respectively. The effects of inorganic admixture content on the performance of both systems were analyzed. Results show that the mechanical properties and water resistance are improved after adding a certain proportion of mineral admixtures to HG. The mechanical properties and water resistance of the HG-PC-FA-HL system are better than the HG-PC system. At the content of 9 wt% FA, 20 wt% PC, and 4 wt% HL, the 28-day strength reaches 41.07 MPa (5955 psi), the water absorption after soaking for 48 h is 12.7 %, and the softening coefficient is 0.72.

This study aimed to evaluate the effect of isolated silica fume (SF) and SF combined with three contents of crystalizing admixture (CA) in the self-healing of engineered cementitious composites (ECCs) with different polymeric fibers. Self-healing was evaluated in coupon specimens subjected to bending to produce cracking. Healing products were evaluated in the cracks within 84 days. Exposure conditions for self-healing were water-saturated (SAT) and wet-dry cycles (WD). The results showed that the composites with isolated SF presented a continuous layer of healing product covering widths of up to 100 μm. The final widths for these composites were 40 μm for different conditions. In composites with CA, the volume of product generated (gel) was considerably greater, causing it to leak out of the microcracks existing in the ECC, impairing healing. Thus, the results showed that the use of SF+CA reduced the ECC healing potential. Healing from the crystallizing admixture was spot-wise only, decreasing its healing potential. The performance of the crystallizing additive was impaired under wetting and drying conditions. Leaching was observed both under SAT and WD exposure conditions. More leaching was observed from WD, while SAT formed a more uniform product layer.

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.

The production of Ordinary Portland Cement (OPC) is a major contributor to carbon emissions. One immediate and viable solution is the use of optimized concrete mixtures that employ a decreased quantity of cement and increased dosage of high-range water-reducing (HRWR) admixtures. This study investigates five different concrete mixtures with varying w/c (0.37 to 0.42) and reduced cement contents. The mixtures with “low cement + high dosage HRWR admixture” content had over 30% increase in mechanical strength and presented 40% lower water absorption, and 68 to 97% higher formation factor, indicating enhanced durability. The optimized concrete mixtures with reduced cement and lower w/c have a service life increase of up to 117% and a life-cycle cost reduction of 29%. The application of “low cement + high dosage HRWR admixture” mixtures can improve the sustainability of concrete mixtures by reducing cement and water contents and increasing the service life of concrete in severe environments.