Effects of Environment in the Microstructure and Properties of Sustainable Mortars with Fly Ash and Slag after a 5-Year Exposure Period
TL;DR: In this article, the effects of exposure to different non-optimum laboratory conditions in the microstructure, mechanical and durability properties of mortars made with slag and fly ash commercial cements were analyzed.
Abstract: Nowadays, getting a more environmentally sustainable cement production is one of the main goals of the cement industry. In this regard, the use of active additions, like fly ash and ground granulated blast-furnace slag, has become very popular. The behaviour, in the short-term, of cement-based materials with those additions is well-known when their hardening is produced under optimum conditions. However, real structures are exposed to different environments during long periods, which could affect the development of microstructures and the service properties of cementitious materials. The objective of this work is to analyse the effects in the long-term (up to 5 years approximately) produced by the exposure to different non-optimum laboratory conditions in the microstructure, mechanical and durability properties of mortars made with slag and fly ash commercial cements. Their performance was compared to that observed for ordinary Portland cement (OPC) mortars. The microstructure has been analysed using mercury intrusion porosimetry. The effective porosity, the capillary suction coefficient, the chloride migration coefficient and mechanical strengths were analysed too. According to the results, mortars prepared using slag and fly ash sustainable commercial cements, exposed to non-optimum conditions, show a good performance after 5-years hardening period, similar or even better than OPC mortars.
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TL;DR: In this paper, a systematic experimental program was designed to assess the most favorable conditions of burning and grinding for pozzolanic activity of wheat straw ash (WSA) in a controlled environment and use the resulting ash as a replacement of cement in cement-based composites.
Abstract: The open burning of biomass residue constitutes a major portion of biomass burning and leads to air pollution, smog, and health hazards. Various alternatives have been suggested for open burning of crop residue; however, each of them has few inherent drawbacks. This research suggests an alternative method to dispose wheat straw, i.e., to calcine it in a controlled environment and use the resulting ash as a replacement of cement by some percentage in cement-based composites. When wheat straw, an agricultural product, is burned, it is very rich in SiO2, which has a pozzolanic character. However, the pozzolanic character is sensitive to calcination temperature and grinding conditions. According to the authors’ best knowledge, until now, no systematic study has been devised to assess the most favorable conditions of burning and grinding for pozzolanic activity of wheat straw ash (WSA). Hence, a systematic experimental program was designed. In Phase I, calcination of WS was carried out at 500 °C, 600 °C, 700 °C, and 800 °C for 2 h. The resulting ashes were tested for color change, weight loss, XRD, XRF, Chapelle activity, Fratini, and pozzolanic activity index (PAI) tests. From test results, it was found that beyond 600 °C, the amorphous silica transformed into crystalline silica. The WSA calcined at 600 °C was found to satisfy Chapelle and Fratini tests requirements, as well as the PAI requirement of ASTM at 28 days. Therefore, WSA produced at 600 °C (WSA600) showed the best pozzolanic performance. In Phase II, WSA600 was ground for various intervals (15–240 min). These ground ashes were tested for SEM, Blaine fineness, Chapelle activity, Fratini, and PAI tests. From test results, it was observed that after 120 min of grinding, there was an increase of 48% in Blaine surface area, with a consequence that WSA-replaced cement cubes achieved a compressive strength almost similar to that of the control mix. Conclusively, wheat straw calcined at 600 °C and ground for 120 min was found to be the most effective way to use pozzolanic material in cement-based composites. The addition of WSA in cement-based composites would achieve manifold objectives, i.e., aiding in the production of environmentally friendly concrete, the use of wheat straw as fuel for electricity production, and adding economic value to wheat straw.
46 citations
TL;DR: In this article, the influence of different curing conditions (wet, dry, and protection against water evaporation) on selected properties of concretes with different amounts of recycled concrete aggregate (RCA) previously subjected to atmospheric CO2 sequestration was presented.
Abstract: The paper presents the influence of different curing conditions—wet, dry, and protection against water evaporation (PEV)—on selected properties of concretes with different amounts of recycled concrete aggregate (RCA) previously subjected to atmospheric CO2 sequestration. Two types of cement were used, Portland cement and blast-furnace slag cement. The study was performed in laboratory conditions (at the temperature of 20 ± 1 °C and relative humidity of about 60%), according to currently applicable test procedures for most of the measured characteristics of concrete. Additionally, the eco-efficiency indexes (bi and ci) as well as the eco-durability S-CO2 index were calculated. It was found that dry conditions cause the properties of concrete to deteriorate, especially concrete made of blast-furnace slag cement, while PEV allows the achievement of results comparable to wet conditions. Moreover, for series with the highest amounts of coarse recycled aggregate and after longer periods of curing, the difference between the effects of wet curing and protection against water evaporation disappears. The eco-efficiency and eco-durability indexes approach confirms the beneficial effect of blast-furnace slag cement used as a binder, but on the condition of using a proper way of curing.
15 citations
18 May 2019
TL;DR: In this paper, an experimental study was made on the effects of using Rice Straw Ash (RSA) and Wheat straw Ash (WSA) as partial replacements of cement in mortar.
Abstract: In this paper an experimental study was made on the effects of using Rice Straw Ash (RSA) & Wheat Straw Ash (WSA) as partial replacements of cement in mortar. The objects were to produce Nano Silica (NS) form RSA & WSA as agricultural wastes by using chemical acids. Then, control specimens with Ordinary Portland Cement (OPC) was made and in other specimen’s cement were replaced with 5%, 10%, 15% and 20% of RS & WS ashes by weight of cement. The workability was measured by the slump test. The pulse velocity and the sorptivity were also computed. The compressive and tensile strengths were also estimated. Experimental result showed that it was feasible to produce silica from WSA by chemical activation method. Also, the highest compressive strength, tensile strength and sorptivity noticed at 15% WSA.
13 citations
Cites background from "Effects of Environment in the Micro..."
..., for their use in cement based composites [14-19]....
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26 May 2020
Abstract: The paper presents the influence of different curing conditions—wet, dry, and protection against water evaporation (PEV)—on selected properties of concretes with different amounts of recycled concrete aggregate (RCA) previously subjected to atmospheric CO2 sequestration. Two types of cement were used, Portland cement and blast-furnace slag cement. The study was performed in laboratory conditions (at the temperature of 20 ± 1 °C and relative humidity of about 60%), according to currently applicable test procedures for most of the measured characteristics of concrete. Additionally, the eco-efficiency indexes (bi and ci) as well as the eco-durability S-CO2 index were calculated. It was found that dry conditions cause the properties of concrete to deteriorate, especially concrete made of blast-furnace slag cement, while PEV allows the achievement of results comparable to wet conditions. Moreover, for series with the highest amounts of coarse recycled aggregate and after longer periods of curing, the difference between the effects of wet curing and protection against water evaporation disappears. The eco-efficiency and eco-durability indexes approach confirms the beneficial effect of blast-furnace slag cement used as a binder, but on the condition of using a proper way of curing.
10 citations
TL;DR: In this article, the influence of replacing natural aggregate with several construction and demolition wastes (C&DW) as recycled aggregate, as well as the use of fly ash and slag, wastes produced in Gas Incinerator Combined Cycle (GICC) thermal power plants, in the mix design of non-structural concrete was investigated.
Abstract: Industrial wastes are often used as aggregate in concrete production to promote a more sustainable construction and to reduce production costs. This article presents the results of an experimental campaign on the influence of replacing natural aggregate with several construction and demolition wastes (C&DW) as recycled aggregate, as well as the use of fly ash and slag, wastes produced in Gas Incinerator Combined Cycle (GICC) thermal power plants, in the mix design of non-structural concrete. Different percentages of natural aggregates were substituted with recycled aggregates either coming from construction and demolition wastes, or from the coarse fraction of the slags from thermic plants in the manufacture of concrete. The mechanical properties, capillary water absorption, density, carbonation, chloride ingress and sulphate resistance have been tested. The results show a decrease in properties when C&DW are used. Fine fraction of slag and fly ash has an important advantage, and can even improve the long term properties of concrete prepared with natural aggregates. Coarse fraction of slag as a recycled aggregate generally improves most of the properties of manufactured concretes.
6 citations
References
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TL;DR: In this paper, the performance of slag, fly ash, and silica fume concretes under four different curing regimes was investigated and the compressive strength was determined at various ages, and the resistance to chloride-ion penetration was measured according to ASTM C 1202 at different ages up to 180 days.
Abstract: This paper reports an investigation in which the performance of slag, fly ash, and silica fume concretes were studied under four different curing regimes. The water-cementitious materials ratio of all the concrete mixtures was kept constant at 0.50, except for the high-volume fly ash concrete mixture, for which the ratio was 0.35. The concrete specimens were subjected to moist curing, curing at room temperature after demoulding, curing at room temperature after two days of moist curing, and curing at 38 °C and 65% relative humidity. The compressive strength was determined at various ages, and the resistance to chloride-ion penetration was measured according to ASTM C 1202 at different ages up to 180 days. Mercury intrusion porosimetry tests were performed on the 28-day old mortar specimens for comparison purposes. The results indicate that the reduction in the moist-curing period results in lower strengths, higher porosity and more permeable concretes. The strength of the concretes containing fly ash or slag appears to be more sensitive to poor curing that the control concrete, with the sensitivity increasing with the increasing amounts of fly ash or slag in the mixtures. The incorporation of slag or silica fume, or high volumes of fly ash in the concrete mixtures, increased the resistance to chloride ions and produced concretes with very low permeability.
403 citations
"Effects of Environment in the Micro..." refers background or result in this paper
...Nevertheless, in the middle- and long-term the lack of enough water in the environment would prevent that this process continues [31,44]....
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...This is also in keeping with mercury intrusion porosimetry results and it would indicate the negative effect in the long-term caused by an environment with very low relative humidity [31,33,51], previously discussed....
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...Regarding those non-optimum laboratory hardening conditions, there are several researches where slag and fly ash cementitious materials were kept under different constant temperature and relative humidity [29–37] and most of them concluded that overall the performance of those materials was adequate [30,31,33–35,38], mainly when the condition presented relatively high values of those environmental parameters [30,31]....
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...This also agree with mercury intrusion porosimetry results, which would indicate the deleterious effect in the very-long term as a consequence of the low availability of water in the environment, hindering the hydration and pozzolanic reactions [31,44] and causing the possible formation of shrinkage microcracks [51]....
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...Nevertheless, the very low relative humidity would not permit the further progression of this process [30,31,33]....
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TL;DR: In this paper, a typical low-calcium fly ash was used as additive in mortar, replacing part of the volume either of Portland cement or aggregate, and the development of the strength, heat, porosity, bound water, and calcium hydroxide content was measured.
398 citations
TL;DR: In this paper, the use of ground granulated blast furnace slag and powder coal fly ash as an addition to either concrete or concrete is well-established and concrete made with these secondary raw materials as a part of the binder does show distinctive advantages over concrete with Portland cement only, especially, the performances with respect to chloride-initiated corrosion of rebars, alkali-silica reaction and sulphate attack are substantially improved.
328 citations
"Effects of Environment in the Micro..." refers background or result in this paper
...For all the environments, the higher Hg retained values corresponded to CEM III mortars, which would agree with their most refined pore network and would reveal the beneficial effects of slag hydration in the pore network development of cementitious materials [7,8,12], even in the very long-term....
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...The lowest total porosities for environment A corresponded to CEM III mortars, while this parameter was very similar for CEM I and II mortars and a little higher for CEM IV ones, which would be in keeping with other authors [7]....
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...Under those conditions, they showed a better behaviour compared to cement-based materials prepared using ordinary Portland cement (OPC) without any addition [7]....
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...On one hand, for slag this result is related to the hydration reactions of this addition, which form new CSH phases, entailing a more refined pore network [7,8,10]....
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01 Jan 2004
TL;DR: In this paper, the authors present a brief review of the theory and construction practice with concrete mixtures that contain more than 50% fly ash by mass of the cementitious material, and the mechanisms by which the incorporation of high volume of the ash in concrete reduces the water demand, improves the workability, minimizes cracking due to thermal and drying shrinkage, and enhances durability to reinforcement corrosion, sulfate attack, and alkalile-silica expansion.
Abstract: This paper presents a brief review of the theory and construction practice with concrete mixtures that contain more than 50% fly ash by mass of the cementitious material. The mechanisms by which the incorporation of high volume of the ash in concrete reduces the water demand, improves the workability, minimizes cracking due to thermal and drying shrinkage, and enhances durability to reinforcement corrosion, sulfate attack, and alkalile-silica expansion are discussed. This technology can play a huge role in meeting the large demand for infrastructure in a sustainable manner for countries like China and India.
325 citations
"Effects of Environment in the Micro..." refers result in this paper
...These more sustainable binders can be used without reductions of the mechanical strength, at least in the long term and sometimes with improvements of the durability properties of the hardened cementitious materials, in agreement with previous results [54]....
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...The present results give further evidence that it is possible to use cementitious materials for concrete elements and structures with a high level of replacement of Portland cement clinker by active additions, such are fly ash and ground granulated blast furnace slag [54]....
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TL;DR: In this paper, the normal consistency, setting time, workability and compressive strength results of Portland cement-fly ash-silica fume systems were reported, and the results showed that water requirement for normal consistency was found to increase with increasing SF content while a decrease in initial setting time was found.
324 citations