- Award ID(s):
- NSF-PAR ID:
- Date Published:
- Journal Name:
- Transportation Research Record: Journal of the Transportation Research Board
- Medium: X
- Sponsoring Org:
- National Science Foundation
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To promote the sustainable development of eco-efficient calcium sulfoaluminate (CSA) cements through the partial replacement of the CSA clinker with supplementary cementitious waste products, the effects of coal fly ashes on the early-age and mature-age properties of a calcium sulfoaluminate (CSA)-based cement paste were investigated. The impacts of both Class C and Class F fly ashes on the rheological properties, hydration kinetics, and compressive strength development of CSA cement paste were studied. Rheology-based workability parameters, representing the rate of loss of flowability, the rate of hardening, and the placement limit, were characterized for the pastes prepared with fixed water-to-cement (w/c) and fixed water-to-binder (w/b) ratios. The results indicate a slight improvement in the workability of the CSA paste by fly ash addition at a fixed w/b ratio. The isothermal calorimetry studies show a higher heat of hydration for the Class C fly ash-modified systems compared to the Class F-modified systems. The results show that fly ash accelerates the hydration of the calcium sulfoaluminate cement pastes, chiefly due to the filler effects, rather than the pozzolanic effects. In general, ettringite is stabilized more by the addition of Class F fly ash than Class C fly ash. Both fly ashes reduced the 1-day compressive strength, but increased the 28-day strength of the CSA cement paste; meanwhile, the Class C modified pastes show a higher strength than Class F, which is attributed to the higher degree of reaction and potentially more cohesive binding C-S-H-based gels formed in the Class C fly ash modified systems. The results provide insights that support that fly ash can be employed to improve the performance of calcium sulfoaluminate cement pastes, while also enhancing cost effectiveness and sustainability.more » « less
Low cost and high durability have made Portland cement the most widely‐used building material, but benefits are offset by environmental harm of cement production contributing 8–10% of total anthropogenic CO2gas emissions. High sulfur‐content materials (HSMs) are an alternative that can perform the binding roles as cements with a smaller carbon footprint, and possibly superior chemical, physical, and mechanical properties. Inverse vulcanization of 90 wt% sulfur with 10 wt% canola oil or sunflower oil to yield CanS or SunS, respectively. Notably, these HSMs prepared at temperatures ≤180 °C compared to >1200 °C hours for Portland cement CanS was combined with 5 wt% fly ash (FA), silica fume (SF), ground granulated blast furnace slag (GGBFS), or metakaolin (MK) to give composites CanS‐FA, CanS‐SF, CanS‐GGBFS, and CanS‐MK, respectively. The analogous protocol with SunS likewise yielded SunS‐FA, SunS‐SF, SunS‐GGBFS, and SunS‐MK. Each of these HSMs exhibit high compressive mechanical strength, low water uptake values, and exceptional resistance to acid‐induced corrosion. All of the composites also exhibit superior compressive strength retention after exposure to acidic solutions, conditions under which Portland cement undergoes dissolution. The polymer cement‐pozzolan composites reported herein may thus serve as greener alternatives to traditional Portland cement in some applications.
Abstract A novel method is developed for reusing the waste glass fiber-reinforced polymer (GFRP) powder as a precursor in geopolymer production. Several activation parameters that affect the workability and strength gain of GFRP powder-based geopolymers are investigated. The results of an experimental study reveal that the early strength of GFRP powder-based geopolymer pastes develops slowly at ambient temperature. The highest compressive strength of GFRP powder-based geopolymer pastes is 7.13 MPa at an age of 28 days. The ratio of compressive strength to flexural strength of GFRP powder-based-geopolymers is lower than that of fly ash and ground granulated blast furnace slag (GGBS)-based geopolymers, indicating that the incorporation of GFRP powder can improve the geopolymer brittleness. GGBS is incorporated into geopolymer blends to accelerate the early activity of GFRP powder. The binary geopolymer pastes exhibit shorter setting times and higher mechanical strength values than those of single GFRP powder geopolymer pastes. The GGBS geopolymer concrete mixture with 30 wt% GFRP powder displayed the highest compressive strength and flexural strength values and was less brittle. The developed binary GFRP powder/GGBS-based geopolymers reduce the disadvantages of single GFRP powder or GGBS geopolymers, and thus, offer high potential as a building construction material.more » « less
This study evaluated the potential of producing supplementary cementitious materials (SCMs) using London Clay excavated from construction activities of the High Speed 2 rail project. A trade-off between enhancing reactivity versus decomposition of impurities (e.g., pyrite, carbonates) present in different London Clay samples was considered in selecting the calcination temperature. The additional reactivity obtained by calcining at 800 °C is deemed to be worth the cost of the small additional process emissions from decomposition of carbonate minerals. Blended cement formulations were developed with the produced SCMs, with replacement levels of 50 and 70 wt%. The optimal gypsum dosage was found to be 1 wt%, which resulted in improved reaction kinetics at early ages. Mortars produced with these binders developed ~50 MPa compressive strength after 90 days of curing even with 70 wt% replacement, which is sufficient for potential production of low to medium strength concretes. These findings demonstrate the excellent potential of London Clays for SCM production and present a systematic approach for characterisation, processing and utilization of excavated mixed clays obtained from infrastructure projects.
This paper aims to clarify the influence of different types of fly ash on the mechanical properties and self-healing behavior of Engineered Cementitious Composite (ECC). Five types of fly ash with different chemical and physical properties were used in ECC mixtures. The fly ash to cement ratio was fixed at 3.0. The compressive and uniaxial tensile tests were conducted to evaluate the influence of fly ash type on mechanical properties. The permeability test was used to assess self-healing behavior of ECCs with different types of fly ash. The microtopography and chemical characteristics of the self-healing products in the crack were observed and examined by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The fly ash with relatively higher calcium content and smaller particle size was found conducive to a higher compressive strength. The lower combined Al2O3 and CaO content of this fly ash, however, was found to enhance the tensile strain capacity. Furthermore, high calcium fly ash accelerates the self-healing process of ECC for the same pre-damaged level. The self-healing product was a mixed CaCO3/C-S-H system with the CaCO3 as the main ingredient.more » « less