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
Influence of fly ash type on mechanical properties and self-healing behavior of Engineered Cementitious Composite (ECC)
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
- Award ID(s):
- 1634694
- NSF-PAR ID:
- 10148590
- Date Published:
- Journal Name:
- FramCos-9
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This study characterized and evaluated the use of reclaimed fly ash (RFA) and reclaimed ground bottom ash (GBA) as alternative sources of supplementary cementitious materials (SCMs) for the production of concrete mixtures. Conventional Class F fly ash (FA) was also evaluated for comparison. The effects of SCM content on fresh and hardened properties of concrete were investigated by replacing 10%, 20%, and 30% of cement by mass. Characterization results showed that all three ashes met ASTM C618 chemical requirements (i.e., sum of SiO 2 + Al 2 O 3 + Fe 2 O 3 , CaO, SO 3 , moisture content, and loss of ignition) and 7- and 28-days strength activity index (SAI) requirements for Class F FA. In addition, RFA exhibited slightly higher SAI at 28 days of curing, followed by GBA and FA. In relation to fresh concrete properties, FA increased the concrete slump compared with the control mixture, whereas RFA and GBA decreased the concrete slump. However, GBA produced more significant slump decrements than RFA, which was attributed to the irregular angular particles of GBA. Generally, all the coal ashes produced decrements in air content compared with the control mixture. Comparatively, among the three ashes, GBA exhibited the highest 28- and 90-days compressive strength and surface resistivity (SR) at all cement replacement levels. Furthermore, at 90 days of curing, RFA and GBA concrete mixtures outperformed the FA concrete mixtures in relation to compressive strength and SR. Consequently, both RFA and GBA are promising SCMs for concrete materials.more » « less
-
This study reports on the self-healing capability of a strain-hardening fiber reinforced geopolymer composite, named Engineered Geopolymer Composite (EGC). EGC specimens were first uniaxially loaded to a tensile strain of 1%. The cracked specimens were then subjected to three different conditioning regimes: air curing, water curing, and no curing (i.e. reloading right after the preloading). Stiffness reduction was measured for each series by comparing the initial stiffness of intact specimens and the residual stiffness of the cracked specimens. In the water-cured specimens, white precipitates were observed in microcracks formed by preloading. Experimental results of the series showed significant stiffness recovery for low stress levels in the range of 0.5 – 1.0 MPa. Self-healing products observed by using a scanning electron microscope were mostly angular, stone-like substance. An analysis of energy dispersive spectroscopy showed that the healing products were relatively rich in silicon (Si) and aluminium (Al) and had lower concentration of calcium (Ca), compared to the geopolymer matrix phase. This implies that main product of EGC self-healing is unlikely to be either calcite (CaCO3) or salt deposits such as Na2CO3, but rather a formation of some aluminosilicate compounds. This study provides a baseline for further investigations into the development of geopolymer composites with robust self-healing.more » « less
-
null (Ed.)Alkali-activated materials (AAMs) are one type of sustainable alternative for ordinary Portland cement (OPC), providing significant reductions in CO2 emissions. AAMs based on fly ash or metakaolin are found to possess good fire performance, where the binder gels crystallize and form ceramic phases on heating. However, the ambient temperature setting properties and short-term strength development of select low-calcium AAMs are unfavorable, requiring the optimization of the mix design and a re-evaluation of the chemical, mechanical and physical properties at elevated temperatures (i.e., fire conditions). In this investigation, the influence of calcium hydroxide on the thermal evolution of alkali-activated metakaolin has been assessed, where gel crystallization and restructuring have been evaluated using X-ray diffraction and Fourier transform infrared spectroscopy. It is found that the 10 wt. % replacement of metakaolin with calcium hydroxide, together with a reduction in silicate activator concentration from 10 to 5M, does not adversely impact the phase evolution on heating since similar crystalline phases are seen to emerge. However, the exact location of calcium in the high temperature phases of silicate-activated metakaolin remains unknown.more » « less
-
more » « less
Abstract 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.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.21012/FC9.209
