International Concrete Abstracts Portal

The uncontrolled urban development of the last century caused high land consumption and strong non-renewable natural raw materials utilization. To solve the problems generated by soil sealing, the building sector has developed a pervious concrete manufactured with Portland cement and natural aggregates. Although this mixture mitigates the effects of soil sealing, the production of a Portland-based pervious concrete has a strong environmental impact.

The purpose of this research is to investigate an alkali-activated slag-based pervious concrete (AASPC) manufactured with tunnel muck (TM) as recycled aggregate instead of natural sand and gravel and to evaluate the relationship between aggregate size and physico-mechanical properties of no-fines concrete.

Six different single-sized recycled aggregates from tunneling works (drilling and blasting technique) were used to produce six different AASPCs that were characterized in terms of compressive strength, porosity, and water permeability under constant and variable flow.

Experimental results evidenced that the average size of aggregates strongly influences the open and total porosity of the materials, thus determining very different compressive strengths (from about 6 MPa for concrete with 16-22 mm gravel to 20 MPa for concrete made with 1-2 mm sand) and water permeability. Finally, the environmental impact of these mixtures (energy requirements, CO₂ emissions, and natural raw materials consumption) is strongly reduced in comparison to traditional Portland-based no-fines concrete at equal strength class.

The new San Giorgio bridge replaced the Polcevera viaduct, built between 1963 and 1967 and collapsed during a storm in summer 2018. The new bridge was designed by Renzo Piano and is made by 19 steel spans supported by 18 concrete pillars. Beside the architectural aspects, special attention was devoted to the mix-design of the pillars, to ensure the production of durable concrete in the marine environment. The use of slag cement combined with limestone filler and polycarboxylate superplasticizers allowed to cast flowable concrete associated with low water to cement ratio and high final compressive strength. A new generation accelerating admixtures, working on the homogeneous nucleation technology, was used to accelerate the cement hydration and gain early compressive strength to speed-up the elevation of the pillars. In the present paper, the advantage of using the new admixture is discussed both in terms of early strength development and microstructure of the cement paste. Beside the improvement of the early strength development, the new admixture reduced the water permeability and the chloride diffusion and improved the resistance to carbonation of the concrete used for the pillars, with further advantages for the durability of this structure.

In order to improve the durability of concrete, a novel waterproofing agent was developed and its effect on concrete performance was studied in detail. Through the research, it is found that when stearic acid is present in the form of ammonium salt in the waterproofing agent, concrete has the highest compressive strength and the best waterproof performance, and the optimum n_NH3: noctadecanoic acid is 1.34, woctadecanoic acid: wamines is 6.45. When the dosage of the waterproofing agent in concrete is 10-30 kg/(1 m³ concrete), the 48h water absorption rate of concrete is reduced by 44.7%~57.4%, and strength increases by at least 30%. By comparing with other waterproofing agents of the same type at home and abroad, it is found that the waterproofing agent provided in this paper has the lowest chloride ion permeability, concrete compactness, and water absorption. After adding a waterproofing agent to the concrete, the chloride migration coefficient and electric flux of concrete are reduced, and the reduction was 37.7% and 22.6%, respectively. The waterproofing agent is a solid-liquid mixture.

The huge quantity of natural aggregates extracted every year and used in the concrete industry is causing harmful consequences on biodiversity, water turbidity, water table level and landscape, and global warming as well. In this context, many studies focused on the possibility to use waste tyre recycled aggregates as partial replacement for stone aggregates in concrete production. Generally, it has been observed that several mechanical properties, such as compressive strength and modulus of elasticity, significantly decrease when rubber content is increased. On the other hand, rubberized concrete (RuC) showed a more ductile behavior than ordinary Portland cement concrete, in addition to a greater damping and energy dissipation capacity. In this paper, the compressive and flexural strength, water permeability, and thermal conductivity of five concrete mixtures with increasing percentages of rubber particles as a partial replacement for natural aggregates have been investigated. As a result, a reduction in compressive strength has been observed only in RuC mixtures with substitutions greater than 12% of the total aggregates, whereas the flexural strength remained roughly constant. Moreover, the results of water permeability and thermal conductivity tests showed respectively a decrease in water penetration and an improvement of the concrete thermal isolation due to the presence of rubber particles.

During the diagnostics of 100-year-old concrete bridges carried out between 2014 and 2022-4 mm (0.078- 0.157 in.) protective render coats (PRC) were found on nine bridges in Slovakia. Most of the PRCs measured appeared almost impermeable, showing a permeability coefficient below 0.246 × 10-16 m2 (0.293 × 10-16 yd.2). At these sites, the underlying concrete was carbonated to a depth of 0 up to 2 mm (0.078 in.), while under spalled PRC was the measured depth of carbonation of concrete up to 80 mm (3.15 in.). The field experiments were followed in a laboratory by the development of PRC from currently available materials. The newly-developed PRCs are characterized by a high weight ratio of ordinary Portland cement (OPC) to natural silica sand, low water content, and, at the same time, capable of being applied in thin layers. The PRCs were applied to a surface of a concrete panel and were tested for permeability (the Torrent method), adhesion (the square target method), crack propagation, microstructure, and pore structure. The resistance to carbonation of the C20/25 strength class (2900/3625 psi) base concrete and those that were PRC-protected were verified by an accelerated carbonation test [20 °C (68 °F)/60% RH/20% vol. CO2].