Search

• Setting time and engineering properties of BCSA concrete are studied. • Citric acid delays initial set from 15 min to as long as 3.5 h. • Retarding hydration does not affect the mechanical strength. • Design codes accurately predict the modulus of elasticity and tensile strength. This paper discusses the setting time and engineering properties (compressive strength, tensile strength, and modulus of elasticity) of belitic calcium sulfoaluminate (BCSA) cement and concrete. BCSA is an emerging alternative cement known for, among other things, its rapid setting behavior. This has long supported its use as a concrete repair material, but BCSA is also attractive for structural applications. Nevertheless, little information is available on the engineering properties of BCSA concrete. This paper quantifies the influence of mixture parameters on BCSA cement setting times, showing that they can be tightly controlled by altering the dosage of a citric acid retarder. It also quantifies the influence of mixture parameters and curing age on compressive strength, proposing predictive models and showing that retarding the hydration of BCSA does not affect its long-term strength. Finally, this paper measures the modulus of elasticity and tensile strength of BCSA concrete and attempts to predict these properties based on the compressive strength. Results suggest that predictive equations from ACI 318, CSA A23, and Eurocode-2 tend to predict the engineering properties of BCSA cement rather well. Together, these results support the feasibility of integrating BCSA cement into practical concrete construction. [ABSTRACT FROM AUTHOR]

• CLSM made using silty soil as only aggregate is feasible for structural fills. • The flowability of CLSM decreases with the increasing RM content. • The optimal mass ratio of RM/cement is 0.5 for engineering properties of CLSM. The aim of this paper is to investigate the feasibility of controlled low-strength materials (CLSM) made from silty soil as the only aggregate, together with local red mud (RM) and portland cement as binder on structural fills. The results indicate that water to solid ratio of 0.46 satisfies the flowability and initial setting time demand, and the RM content less than 7.5% satisfies the strength and impermeability demand. RM has a significant influence on the engineering properties of CLSMs. At 3 d, the properties containing unconfined compressive strength, direct shear strength, and impermeability decrease with the increase of RM content. However, these properties initially increase and then decrease with the increase of RM content from 7 to 28 d, the optimum mass ratio of RM to cement is 0.5. The mechanism is summarized as a filler effect, an alkali environment effect, and a pozzolanic effect. [ABSTRACT FROM AUTHOR]

• Healing efficiency theory developed based on geometric probability. • New self-healing capsules, called engineered aggregates, are introduced. • Self-healing efficiency calculated for different cracking conditions. • Effect of size, shape and dosage of capsules on healing efficiency is evaluated. This paper presents optimal self-healing configurations in concrete using a new concept referred to herein as engineered aggregates (EA). EA are hollow particles designed to carry healing agents into the cracks in concrete. The concept of EA has been developed by the authors as a cost-effective method for self-healing in conventional concrete without having to modify the existing materials or mixing procedures. EA have an internal brittle capsule carrying the healing agents and they are covered with a cementitious coating. They are similar in size to a concrete coarse aggregate and they are added during the mixing process replacing a portion of the coarse aggregates. Similar to other self-healing materials with cast in capsules, one of the basic requirements of EA is that when concrete cracks, the cementitious coating and the embedded brittle capsule break to release the healing agents into the cavity of the crack. The goal of this study is to identify the optimal shapes and sizes of EA that can be effectively used in self-healing concrete while minimizing the volume fraction of the added healing agent (and thereby EA). The tools of geometric probability are used to determine the probability of intersection of cracks with EA and the probability of healing of cracks with different geometries: a single crack, parallel cracks, mapping cracks and multiple discrete penny-shape cracks. As such, the optimal size and shape of EA are selected based on the density and type of cracking that might occur in concrete. [ABSTRACT FROM AUTHOR]

[Display omitted] • The PU prepolymers can chemically react with the base asphalt. • The PU has superior high-temperature stability, adhesion strength, and durability to asphalt. • The anti-aging performance of PU sealants is always a great concern. • High-density PU foam injection has been implemented as an alternative to the conventional cement. • PU-bonded mixture can improve the performance and extend the service life of pavements. In the past decades, Polyurethane (PU) as an emerging polymer material has been widely used to construct, repair, reinforce, and protect civil engineering infrastructures. Meanwhile, various PU-based materials are increasingly employed in pavement engineering for new construction and maintenance, due to their excellent physical and chemical properties. In this review paper, the synthesis method, chemical structure, and engineering properties of PU materials were first introduced briefly. Secondly, the practical applications of PU materials in pavement engineering at present were summarized, mainly including PU-modified asphalt, PU-bonded mixture, PU sealant, and PU foam injection. Finally, the potential economic benefits and environmental impacts of utilizing PU materials in pavement engineering were further discussed towards sustainability. [ABSTRACT FROM AUTHOR]