International Concrete Abstracts Portal

In current ACI 318 code, crack control design criterion for prestressed concrete (PSC) members is stricter than conventional reinforced concrete (RC) members. In particular, it is stipulated that the net tensile stress of prestressing strands should be controlled under 250 MPa (36.3 ksi) in the serviceability design of PSC members belonging to the Class C section that is expected to be cracked under service load conditions. To this end, the nonlinear cracked section analysis is essentially required to estimate the tensile stress of the prestressing strands under the service loads, which requires cumbersome iterative calculations in practice. This study aims to propose a simplified method to estimate the net tensile stress of the prestressing strands (Δfps) under the service load conditions and also a tabulated checking method whether the net tensile stress (Δfps) exceeds the stress limit with respect to the magnitude of effective prestress (Δfse). Finally, applicability of 2,400 MPa (348 ksi) Grade strands is also experimentally investigated.

As the concrete, cement, and wider construction industries around the world move toward net-zero emissions, many alternative concrete and cement technologies have emerged with the intention of reducing the embodied carbon (EC) of concrete. Concretes have been labeled as “sustainable” and “low carbon,” and such terms have been used inconsistently. This article introduces an EC classification system.

This paper examines the influence of harvested fly ash on the properties of mortar and concrete. Class F and harvested fly ash were used at the substitution rate of 20% by weight of Portland cement. The investigated properties included heat release, consistency, setting time, compressive strength at different testing ages, absorption, the volume of permeable voids, surface resistivity, and drying shrinkage. The results revealed that the harvested fly ash produced the lowest released heat of hydration and longest setting times. Mixtures containing harvested fly ash displayed lower strength at all curing ages. Compared to traditional fly ash, harvested fly ash showed inferior transport properties for both absorption rate, permeable voids, and surface resistivity. Mixtures containing harvested fly ash showed comparable 120-day drying shrinkage when compared with the companion mortars made with traditional fly ash.

Due to its predominant soda-lime composition, most post-consumer glass processed by recycling facilities would be classified as high-alkali pozzolanic glass powder (GP). In cementitious matrices, the intrinsic alkaline pore solution induces the dissolution of both silica and alkali ions. Therefore, the GP can potentially induce two similar reactions in concrete: either a deleterious alkali-silica reaction or a pozzolanic reaction. The equilibrium of the pore solution will determine which reaction will prevail in the long term. To understand the chemical stability of GP in a cementitious system, the evolution of the solubility of key elements in an alkali-rich synthetic pore solution was studied as a function of reaction time, particle size, presence of Ca(OH)₂ and CaCO₃, and binder/solution ratio (B/S). The solution was based on the R³ method, which consists mainly of lab-grade chemicals such as KOH and K₂SO₄. Although the chemical equilibrium seems to be fully reached in the first hours of hydration, the main products, such as C-S-H, are unstable because the alkali leaching/uptake in the C-S-H chains is dynamically evolving. The experiments show that both C-S-H precipitation and alkali leaching rates increase with increasing B/S ratio and decreasing particle size, and are directly related to the presence of calcium in the solution.

Approximately 22 kg of spent pot lining is generated (SPL) per ton of aluminum produced by electrolytic cells. Untreated SPL is classified as hazardous industrial waste due to its hydroreactive nature and the presence of leachable cyanide and fluoride compounds. After treatment with the Low Caustic Leaching and Liming (LCL&L) industrial process, the refractory portion of the SPL is transformed into an inert material called LCLL. This project analyzed the use of LCLL as a cement binder. The reactivity of LCLL was studied using the compressive strength activity index, and RILEM R³ tests. The results showed that LCLL is composed of stable crystalline phases such as corundum, albite, and nepheline, and contains graphite. The improvement of LCLL reactivity was explored by calcination and the addition of synthetic fluorite, also from the LCL&L process. The results showed a significant improvement in reactivity with the formation of a larger amount of reactive amorphous phases with high silica and alumina content with optimum fluorite content of 10%. Calcined LCLL showed similar reactivity to fly ash, without retarding effect, with compressive strength equivalent to cement at 112 days and the formation of a new phase rich in carboaluminate.