This research examines the performance of quality-controlled recycled concrete aggregates (QRA) with fly ash-based cement. Compared to concrete made from untreated recycled concrete aggregates (URC), quality-controlled recycled aggregate concrete (QRC) has superior physical, mechanical, and durability properties. Except for sorptivity, the physical, mechanical, and durability properties of QRC are almost identical to those of NC. The compressive strength, split tensile strength, flexural strength, fracture energy, and modulus of elasticity of QRC are higher than those of URC by 18.0, 16.8, 60.0, 27.17, and 43.46 percent, respectively. The abrasion resistance of QRC is around 60 percent higher than URC. Scanning Electron Microscope (SEM) image and Energy Dispersive X-ray (EDX) analysis prove that quality control produces denser old interfacial transition zone (OITZ) with fewer microvoids. The quality-controlled recycled concrete aggregate improves not only the pore structure but also the weak mortar structure attached to the aggregate. There is also a strong correlation between the compressive strength and split tensile strength, flexural strength, fracture energy, and modulus of elasticity of QRC. QRA can be used to compute the mix proportion for concrete (certainly up to medium strength concrete) according to either the Indian Standard or the International Standard. It is challenging to improve the sorptivity of recycled concrete aggregates closer to NC. In addition, QRC has an initial sorptivity of 2 times (initial) and a final sorptivity of 1.8 times higher than NC, whereas URC has an initial sorptivity of 3.5 times (initial) and a final sorptivity of 2.35 times higher than NC.

The penetration of chloride ions causes a degradation of the reinforcement bars, which directly affects the service life of the element. In this study, four different alternatives for the construction of an RC caisson parapet beam are investigated: conventional RC, the addition of a corrosion inhibitor to concrete, and the use of GFRP and galvanized steel instead of steel bars. The durability of the RC element under a marine environment was studied based on both measurements performed in situ and in well-controlled laboratory conditions on specimens prepared in the laboratory, as well as specimens taken from the actual structural element. It was concluded that exposure of fresh concrete to seawater splash has no effect on mechanical properties. In addition, galvanized rods were found to be a less effective protection strategy compared to the other alternatives studied. GFRP bars, however, provide better protection than the other tested alternatives, although chloride ion penetration in these bars was found to be more accelerated in an alkaline environment compared to a chloride environment. In contrast to the prevailing approach which considers the plain concrete and according to which the electrical resistance of the concrete decreases because of chloride penetration, this study found that electrical resistance in the reinforced element is increased due to an increase in the amount of corrosion products formed between steel and concrete, as long as no cracks occur. Furthermore, it was found that the potential measured using the half-cell method in all the alternatives slowly increased in time, as well as the corrosion risk in the three alternatives with reinforcing steel. The remaining question is whether this change of potential is a direct characteristic of the corrosion risk. Therefore, more research in this direction is needed.

This study clarifies the effects of moisture (expressed as percentage saturation degree of permeable pore voids, PSD) on water ingress properties of concrete and establishes a region where PSD does not affect the quantitative water absorption. Experimental measurements and finite element model (FEM) simulation results for ordinary portland cement (OPC) concretes preconditioned to equilibrium moisture formed plateaus between 21 and 58% PSD. Non-continuous finer capillary pores (ϕ10 nm [3.937 × 10–4 mil, thou] to ϕ100 nm [3.937 × 10–3 mil, thou]) constitute the empty pores within the plateau region before tests. Water sorptivity of OPC and slag cement concrete blocks at several degrees of surface moisture with internal moisture gradients validate the existence of the plateau within the PSD range. Measuring short-term water absorption within this plateau region eliminates the effects of initial surface moisture content on the measured properties and evaluates the continuity and connectivity of pores, which is the major indicator of the durability of concrete.

This study proposed using carbon dioxide (CO2) as an indirect admixture for calcined clay blended pastes. By injecting CO2 gas into limewater, solid nano-CaCO3 particles were synthesized and used to partially replace the binder at ratios of 2, 4, and 6%. Various tests and analyses were performed on the calcined clay blended pastes. After adding nano-CaCO3, the strength, ultrasonic pulse velocity, hydration heat, and electrical resistivity were improved; monocarboaluminate and hemicarboaluminate were formed; and CO2 emissions were lowered. The electrical resistivity was improved more significantly than the strength. The reduction ratio in CO2 emissions was higher than the replacement ratio of nano-CaCO3. In summary, based on the transformation of gaseous CO2 to solid nano-CaCO3 particles, the proposed technique shows a similar concept to limestone calcined clay cement (LC3) concrete and can overcome the limitations of carbonation curing.

Self-healing is a process by which concrete is able to recover its properties after the appearance of cracks, which can improve mechanical properties and durability and reduce the permeability of concrete. Self-healing materials can be incorporated into concrete to contribute to crack closure. This study aims to evaluate the influence of crystalline admixtures and silica fume on the self-healing of concrete cracks. The rapid chloride penetration test was performed on cracked and uncracked samples, from which it was possible to estimate the service life of concretes. The concretes were characterized by tests of compressive strength and water absorption by capillarity. The use of crystalline admixtures did not have a negative influence on concrete properties, but did not favor the chloride penetration resistance. The concrete with silica fume showed the lowest charge passed and highest values of estimated service life.