Recently, alkali-activated cement (AAC) has been studied to partially replace portland cement (PC) to reduce the environmental impact caused by civil construction and the cement industry. However, with regard to durability, few studies have addressed the behavior of AAC. This study aimed to evaluate the performance of AAC made from blast-furnace slag with contents of 4 and 5% sodium hydroxide as an activator (Na2Oeq of 3.72% and 4.42%, respectively) when subjected to alkali-aggregate reaction (AAR). Length variation tests were carried out on mortar bars immersed in NaOH solution (1 N of NaOH, T = 80°C [176°F]) and on concrete bars (T = 60°C [140°F], RH = 95%); compressive strengths tests and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses were also made. Two types of PC were used as a comparison. The results showed good behavior of the AAC in relation to the AAR, with expansions lower than those established by the norm (34% of the limit) and without the finding of losses of mechanical resistance or structural integrity. The alkaline activator content had a small influence on the behavior of the AACs, in which the lowest amount of NaOH (4%) showed fewer expansions (only 15% of the limit established by the norm). Even for the highest activator content (5%), the results were good and comparable to those of PC with pozzolans, which is recommended for the inhibition of AAR.

Cross-linked polycarboxylates were synthesized and characterized with Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). A comparative investigation of the mechanism behind the relationship between the molecular structure and performance (in terms of rheology, workability retention, and compressive strength) is the novelty of this research. Presence of cross-linkages in polymer structure provided high workability and workability retaining ability to cement pastes. A moderate cross-link density was determined as an important factor for cement dispersion (cross-link/side chain/main chain units molar ratios are 0.2/0.8/10). On the other hand, compressive strengths of designed concretes were significantly affected from the structure of superplasticizers— namely, highly cross-linked polymer provided better compressive strength (73.5 MPa and 72.5% strength increment to the basis of plain concrete). Finally, it was thought that cross-linked polycarboxylate-type superplasticizers could be the functional alternatives of their traditional counterparts, especially for the applications which required more workability and workability retention.

Penetration sealers are an economically viable technique to reduce water and aggressive substance ingress into concrete, and ultimately extend service life under harsh conditions. This paper discusses a laboratory investigation to assess the effect of rate and application timing of a variety of penetrating sealers on saw-cut concrete. Sealer types included pore lining, pore blocking, and pore refining in addition to surface coating. Testing included absorption, contact angle, and chloride-ion penetration performed on mortar and concrete specimens. Results show sealers significantly reduced water penetration, as expected, with higher rates of application generally resulting in less absorption. Two applications of sealer applied at half the recommended dosage rate produced better performance than a single application at the full dosage rate, even for hydrophobic sealers such as silane. Of the sealers tested, solvent-based and water-based produced the greatest reduction in absorption and chloride penetration. The results show that sealers applied in the appropriate condition and concentration can greatly extend the time to critical saturation by reducing the absorption rate, significantly reduce chloride ingress, and potentially increase the service life of concrete or provide extra protection.

The possibility of incorporating scrap tire residue into concrete has already been consolidated in previous studies, but there is a knowledge gap about how concrete made with recycled tire materials behaves when exposed to high temperatures. This study aims to investigate the performance of precast concrete panels made with scrap tire residues when exposed to fire when using recycled steel fiber and recycled rubber aggregates separately. The experimental design consisted of fire resistance tests. Real-scale panels were exposed to the standard fire curve based on ISO 834, measuring the temperatures on the panel surfaces. The recycled steel fiber-reinforced concrete and those containing 5% recycled rubber aggregate presented similar behavior when compared to the conventional concrete on thermal insulation, integrity, and structural stability. The concrete made with 10% recycled rubber aggregate registered the occurrence of explosive spalling and worse thermal insulation and integrity.

This study investigates the influence of internal curing water on the compressive strength and microstructure of high-performance cementitious materials. For this, three high-performance fine-grained concrete (HPFC) and cement pastes were prepared. Two reference mixtures were investigated with total water-cement ratios (w/c) of 0.30 and 0.35. The third mixture was prepared with a basic w/c of 0.30 and the addition of 0.3% of superabsorbent polymer (SAP), resulting in a total w/c of 0.35. X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and compressive strength tests were performed. The incorporation of SAP resulted in a refinement of the porous structure of the paste, despite increasing the total porosity. In addition, the paste containing 0.3% SAP resulted in an intermediate calcium hydroxide content compared with the reference pastes. Thus, it was concluded that SAP internal curing water participates in the hydration reactions of the cementitious material.