The use of thermal analysis in assessing the effect of temperature on a cement paste
TL;DR: In this article, the effect of temperature in the mineralogical composition of cement hydration products has been studied using thermogravimetric analysis (TGA) and DTG curves, which can be used to determine fire conditions and the consequent deterioration expected in the cement paste.
About: This article is published in Cement and Concrete Research.The article was published on 2005-03-01. It has received 709 citations till now. The article focuses on the topics: Cement & Portlandite.
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TL;DR: The microstructural evolution of alkali-activated binders based on blast furnace slag, fly ash and their blends during the first six months of sealed curing is assessed in this article.
Abstract: The microstructural evolution of alkali-activated binders based on blast furnace slag, fly ash and their blends during the first six months of sealed curing is assessed. The nature of the main binding gels in these blends shows distinct characteristics with respect to binder composition. It is evident that the incorporation of fly ash as an additional source of alumina and silica, but not calcium, in activated slag binders affects the mechanism and rate of formation of the main binding gels. The rate of formation of the main binding gel phases depends strongly on fly ash content. Pastes based solely on silicate-activated slag show a structure dominated by a C–A–S–H type gel, while silicate-activated fly ash are dominated by N–A–S–H ‘geopolymer’ gel. Blended slag-fly ash binders can demonstrate the formation of co-existing C–A–S–H and geopolymer gels, which are clearly distinguishable at earlier age when the binder contains no more than 75 wt.% fly ash. The separation in chemistry between different regions of the gel becomes less distinct at longer age. With a slower overall reaction rate, a 1:1 slag:fly ash system shares more microstructural features with a slag-based binder than a fly ash-based binder, indicating the strong influence of calcium on the gel chemistry, particularly with regard to the bound water environments within the gel. However, in systems with similar or lower slag content, a hybrid type gel described as N–(C)–A–S–H is also identified, as part of the Ca released by slag dissolution is incorporated into the N–A–S–H type gel resulting from fly ash activation. Fly ash-based binders exhibit a slower reaction compared to activated-slag pastes, but extended times of curing promote the formation of more cross-linked binding products and a denser microstructure. This mechanism is slower for samples with lower slag content, emphasizing the correct selection of binder proportions in promoting a well-densified, durable solid microstructure.
736 citations
TL;DR: In this article, the authors addressed the mix design and properties assessment of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) by employing the modified Andreasen & Andersen particle packing model.
615 citations
TL;DR: In this paper, a modified Andreasen & Andersen particle packing model is used to achieve a densely compacted cementitious matrix, and the results show that the influence of FA, ground granulated blast-furnace slag (GGBS) and limestone powder (LP) on the early hydration kinetics of UHPC is very similar during the initial five days, while the hydration rate of the blends with GGBS is mostly accelerated afterwards.
Abstract: This paper addresses the development of an eco-friendly Ultra-High Performance Concrete (UHPC) with efficient cement and mineral admixtures uses are investigated. The modified Andreasen & Andersen particle packing model is utilized to achieve a densely compacted cementitious matrix. Fly ash (FA), ground granulated blast-furnace slag (GGBS) and limestone powder (LP) are used to replace cement, and their effects on the properties of the designed UHPC are analyzed. The results show that the influence of FA, GGBS or LP on the early hydration kinetics of the UHPC is very similar during the initial five days, while the hydration rate of the blends with GGBS is mostly accelerated afterwards. Moreover, the mechanical properties of the mixture with GGBS are superior, compared to that with FA or LP at both 28 and 91 days. Due to the very low water amount and relatively large superplasticizer dosage in UHPC, the pozzolanic reaction of FA is significantly retarded. Additionally, the calculations of the embedded CO2 emission demonstrate that the cement and mineral admixtures are efficiently used in the developed UHPC, which reduce its environmental impact compared to other UHPCs found in the literature.
408 citations
TL;DR: In this article, the authors presented the effect of nano-silica on the hydration and microstructure development of UltraHigh Performance Concrete (UHPC) with a low binder amount.
407 citations
Cites background from "The use of thermal analysis in asse..."
...As commonly known, the hydrated cement paste subjected to an elevated temperature loses the free water, dehydrates and the hydrated products are transferred [39–44]....
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TL;DR: In this paper, two types of nano-TiO2 particles were blended into cement pastes and mortars and their effects on the hydration and properties of the hydrated Cement pastes were investigated.
Abstract: Two types of nano-TiO2 particles were blended into cement pastes and mortars. Their effects on the hydration and properties of the hydrated cement pastes were investigated. The addition of nano-TiO2 powders significantly accelerated the hydration rate and promoted the hydration degree of the cementitious materials at early ages. It was demonstrated that TiO2 was inert and stable during the cement hydration process. The total porosity of the cement pastes decreased and the pore size distribution were also altered. The acceleration of hydration rate and the change of microstructure also affected the physical and mechanical properties of the cement-based materials. The initial and final setting time was shortened and more water was required to maintain a standard consistence due to the addition of the nano-TiO2. The compressive strength of the mortar was enhanced, practically at early ages. It is concluded that the nano-TiO2 acted as a catalyst in the cement hydration reactions.
373 citations
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TL;DR: In this paper, a reassessment of the subject is given, which considers material and environmental factors/mechanisms influencing the strength of concrete during the heat cycle and after cooling, not all of which necessarily result in strength loss.
Abstract: Based on experience with siliceous aggregate/OPC paste concrete it is generally believed that the compressive strength of unsealed ‘concrete’ declines sharply above 300°C. This is too pessimistic a view. A reassessment of the subject is given in this Paper, which considers material and environmental factors/mechanisms influencing the strength of concrete during the heat cycle and after cooling, not all of which necessarily result in strength loss. Design of concrete for better performance at high temperatures should aim at minimizing contributions to strength loss, while exploiting the processes responsible for gain in strength. It appears that, in its hydraulic state of binding, a rheological criterion limits the structural usefulness of Portland cement concrete to temperatures of 600°C. Today, many commonly used concretes lose considerable strength at temperatures above about 300°C. There is, therefore, scope for improvement in design within the temperature range 300— 600°C. Raising the ‘working’ temper...
458 citations
TL;DR: In this article, the decomposition and reformation of ettringite is studied as a function of water vapour pressure and temperature, and the authors make recommendations for the upper safe service limits for ETTringite-based cements.
303 citations
TL;DR: In this paper, the effect of elevated temperatures on the mineralogical changes occurring in the hydrated phases of concrete cubes were studied by measuring ultrasonic pulse velocity (UPV) and consequent deterioration in the compressive strength with increase in temperature.
276 citations
TL;DR: In this article, the thermal behavior of hydration products in ordinary Portland cement as a function of age was investigated using differential scanning calorimeter (DSC) and X-ray diffraction analysis.
228 citations
TL;DR: In this article, high-alumina refractory castables with compositions in the systems CaO-Al2O3 and CaO−Al 2O3-SiO2 were studied using an ultrasonic technique.
Abstract: High-alumina refractory castables with compositions in the systems CaO–Al2O3 and CaO–Al2O3–SiO2 were studied using an ultrasonic technique. The technique allows in-situ, non-destructive measurement of Young's modulus from room temperature to 1600°C. Elastic and dilatometric properties were investigated in relation to phase changes (followed by XRD) and sintering phenomena. The conversion of CAH10, the hydration of still-anhydrous cement phases, and the dehydration of C3AH6 and AH3 are related with events in Young's modulus evolution. Addition of 1 wt% of silica fume strongly decreases the high-temperature mechanical properties.
123 citations