Thermal properties of high-volume fly ash mortars and concretes (original) (raw)
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Thermal Conductivity Studies for Self-Compacting Concrete with Sand and Fly Ash Variation
ACI Materials Journal, 2015
The thermal properties of self-consolidating concrete (SCC) influence its durability performance. Thermal properties (specific heat, coefficient of thermal expansion, and thermal conductivity) of concrete are governed by the thermal properties of the constituent materials. Fine aggregates have a significant role in fresh as well as hardened state properties of the concrete mixture. The availability of natural sand (NS) is limited due to environmental regulations. Crushed sand (CS) is an emerging alternative to NS for concrete preparation. An experimental study was undertaken to measure thermal conductivity (k) values for an M-40 grade SCC mixture, with varying fly ash dosage, prepared with NS and CS. The k values were determined for normal service temperature range of 86 to 176°F (30 to 80°C) using the steady-state method. The experimental results were analyzed and empirical relations between the k value and the density, as well as with temperature, were developed. The 28-day compressive strength for SCC mixtures with CS was 18% and 35% more than the NS concrete mixtures at 0% fly ash and at 40% fly ash addition level, respectively. The k value for the SCC mixtures with CS was 6.25% and 2.38% more than the SCC mixtures with NS at a temperature range of 86 to 104°F (30 to 40°C) and 158 to 176°F (70 to 80°C), respectively, without any fly ash addition. At 40% fly ash addition level, the k value for the SCC mixtures with CS was 26.39% and 4.12% more than NS-based mixtures at 86 to 104°F (30 to 40°C) and at 158 to 176°F (70 to 80°C), respectively. Durability and sustainability of concretes may be enhanced by using CS instead of NS.
Strength and Hydration Heat of Concrete using Fly Ash as a Partial Replacement of Cement
2009
The benefits of using fly ash as a partial replacement for cement in concrete are well documented. This paper presents the strength development and hydration heat properties of concrete using Class F fly ash sourced from Western Australia. Compressive strengths at different ages were determined and semi-adiabatic temperature rise during the initial stage of hydration was measured by thermocouples. The 28-day compressive strengths of two control concrete mixtures were 62 and 68 MPa. It was found from the experimental results that the average 28-day compressive strengths of concretes with 30% and 40% cement replacements by fly ash were 84% and 63% of the strengths of the respective control mixtures. However, the 90-day strength of concrete with 30% cement replacement was equal to the strength of the control concrete. A 20% reduction in the maximum temperature was observed in the concrete with 40% cement replacement by the fly ash. It is found from the test data that the percentage red...
2018
Fly ash and slag are two SCM’s utilized widely as partial replacements of cement in mass concrete. Different chemical, physical properties and reaction behavior cause fly ash-cement blend to differ from slag-cement blend in terms of thermal properties and thermal cracking in mass concrete. In this study, the time-dependent behavior of specific heat, thermal conductivity, and coefficient of thermal expansion (CTE) of hardening cement pastes containing fly ash and slag are comparatively investigated. Time-dependent models are proposed with satisfactory fit to the test results. A detailed comparison is done using finite element analysis of a mass concrete sample to evaluate thermal cracking potential, by comparing the predicted maximum restrained strain to the tested tensile strain capacity. The results indicate that fly ash performs better with lesser thermal cracking potential than slag in concrete mixes designed for similar long-term strengths.
Evaluation of the Effect of Fly Ash on the Cement Heat of Hydration According to Astm C1702
2018
In the construction of mass concrete structures, special attention should be given to the cement heat of hydration (HH). The amount of HH released can be substantial that it might compromise the integrity of the structure. Uncontrolled HH can lead to the formation delayed ettringite formation and thermal stresses that may lead to the failure of the structure. One method to control the HH is through the integration of pozzolanic supplementary cementitious materials (PCSM) in the concrete mix that are known to lower the HH. Previous research shows that Fly Ash (FA) can be an effective replacement of cement especially in mass concreting as it not only enhances the compressive the strength but also it lowers the HH. However, one study shows that heat released using FA class-C can exceed the HH of plain cement. As such, there is a need to investigate this discrepancy and verify the results. This study presents a re-evaluation of the effect of FA on the HH of a cement HH using a high prec...
Properties of cement-based materials containing fly ash
Proceedings of the Second International Conference on Performance–based and Life-cycle Structural Engineering (PLSE 2015), 2015
Fly ash has been increasingly used in concrete structures due to both environmental and technical benefits. Despite significant past research, our understanding of thermal and physical properties of fly ash mortar and concrete remains incomplete and thus needs further investigation. This paper presents results of a study into important fundamental thermal and physical properties of both fly ash mortar and fly ash concrete. Replacement levels of Portland cement by fly ash investigated were30%, 50% and 60% by mass. In cement-fly ash mortar tests, increasing fly ash content was found to delay setting times, decrease both compressive and flexural strengths and reduce hydration heat. The effect of fly ash on hydration heat evolution of cement binder was quantitatively analysed. The obtained reduction coefficient (k) would allow reasonable prediction of temperature rise in concrete structures, which is of particular interest for mass concrete construction. In cement-fly ash concrete tests, thermal properties, including thermal diffusivity, conductivity and specific heat, were also measured and reported. There also appeared a linear relationship between compressive and flexural strengths of
Materials Science, 2016
Thermal properties of cement composite with Mixed Fly Ash (MFA) from different parts of Municipal Solid Waste Incineration (MSWI) process as a partial replacement of Portland cement are researched in the paper. MFA is applied in the amount of 10 %, 20 % and 30 % of the mass of cement, while sand and water quantities are kept constant. For the sake of comparison, a reference mixture with Portland cement as the only binder is studied as well. For the characterization of studied materials, their basic physical properties as bulk density, matrix density and total open porosity are measured using gravimetric method combined with helium pycnometry. Among the thermal properties, thermal conductivity, thermal diffusivity and specific heat capacity are accessed by two transient methods having different experimental arrangement and time of measurement. The measured data obtained by the particular methods are compared and the applicability of the methods for the measurement of thermal properties of solid building materials is discussed.
Thermal Properties of Commercially Available High-Strength Concretes
Cement, concrete and aggregates, 1997
This paper summarizes the thermal properties of commercially available high-strength concretes. Five concretes with anticipated compressive strengths in the range of 1OOOO to 20000 psi (69 to 138 MPa) were tested. WIC ratios ranged from 0.26 to 0.43; water-tetorai cementitious material ratios ranged from 0.22 to 0.32. The concretes, containing either no mineral admixtures, silica fume only, or both fly ash and silica fume, were delivered by a ready-mix supplier for laboratory testing. Tests covered by this paper include thermal conductivity, thermal diffisivity, specific heat, and drying rates. Thermal conductivity was measured using a guarded hot plate (ASTM C 177) at 85, 300, and 700°F (30, 150, and 370°C). Thermal conductivity was also measured using the hot-wire method (ASTM C 11 13) at 70,300,570,840, 1 110, 1380, and 1830°F (25,150,300,450.600,750, and 1ooo"C). Thermal diffisivity was measured, using the guarded hot plate apparatus, at 95, 250, and 500°F (35, 120, and 250°C). Thermal diffusivity was also measured using a dynamic radial heat flow method continuously from 2 10 to I830'F (100 to lO00"C). Thermal propties at high temperatures differed depending on the method used. Specific heat was measured on saturated concrete at ambient temperatures. Rates of drying for initially moist cured specimens were determined by oven-drying thermal conductivity specimens at 150. 185, and 220°F (65,85, and 105°C) prior to thermal testing. Mass loss was measured at temperatures up to 1740°F (950°C) at heating rates of 4,36, and 90°F (2,20, and 50°C) per minute.
Thermo-mechanical properties of concrete containing high-volume mineral admixtures
Building and Environment, 2007
This paper reports the results of a study conducted to evaluate the influence of high-volume class C fly ash (FA), blast furnace slag (BFS) and both FA+BFS on the thermal conductivity (TC), compressive strength, water absorption and density of concrete. TC decreased with the increase of FA, BFS and FA+BFS as replacement for Portland cement. The reductions in TC due to FA, BFS and FA+BFS were, respectively, up to 39%, 18% and 31%. The addition of FA, BFS and FA+BFS in the concrete had a decreasing effect on TC. Their addition also decreased compressive strength as a function of replacement percent. However, this reduction in compressive strength decreased with increasing curing period.
Evaluation of sustainable high-volume fly ash concretes
Cement and Concrete Composites, 2011
In many countries like México, despite the potential benefits of a superplasticized fly ash (FA) concrete being well disseminated in the technical literature, the potential benefits of these two ingredients and their synergetic effect are not exploited by the concrete industry. This article presents results of an experimental research work oriented to develop practical tools for the regional concrete industry, as well as to illustrate the potential benefits of the synergetic effect of an ASTM C 618 Class F FA produced in the Northeast of México and a polycarboxylate superplasticizer (SP) in the production of conventional concrete. The different concretes considered in this study were produced with water/binder (w/b) ratios between 0.5 and 0.6, mass substitutions of cement by FA between 15 % and 75 %, and a target slump of 20 cm ± 2 cm. Sustainability is a key issue in this work; in this regard, the approach was to improve the ability of concrete to diminish its ecological impact, and is based on two main aspects: the highest water reduction through the use of an optimum SP dosage that resulted in reductions of 18 %, 15 % and 11 % respectively for the reference mixtures of w/b=0.5, w/b=0.55, and w/b=0.6, which leads to the same reductions of cement; and the use of conventional to high volumes of FA. Key parameters in the fresh and hardened states were characterized to establish tools that can facilitate the use of these concretes in practice. Heat release and heat flow were analyzed through isothermal and semi-adiabatic calorimetry, illustrating that heat release per unit mass of cement is independent of w/b, contrasting with the time of setting results that vary by several hours between the three different w/b ratios. The paper highlights the beneficial effect of the SP in terms of cement reduction and slump retention. Correlations between the FA substitution and slump loss, setting times, compressive strength and static modulus of elasticity (E) were established and they represent very useful potential tools for practical applications of the results. Compressive strength developments up to an age of 56 d are also reported, as well as correlations between the modulus of rupture and compressive strength or splitting tensile strength at an age of 28 d.
Utilization of fly ash cenosphere to study mechanical and thermal properties of lightweight concrete
AIMS Materials Science, 2020
The utilization of cenosphere by-product of fly ash as a substitution of sand in concrete is an effective way to reduce thermal conductivity. This study investigates the mechanical and thermal properties of cenosphere substituted in the lightweight concrete. Cenosphere is the recycled material and possesses good thermal insulation properties. Study objectified replacement of sand over the FA cenospher to study the mechanical and thermal properties of the concrete. Experimental setup of the study 10%, 20% and 30% sand by weight is replaced with cenosphere. Concrete specimen prepares and cured for the period of 3, 7 and 28 d. Compressive strength of the concrete is analyzed for 3-7 and 28 d where tensile strength is analyzed for 28 d. Study shows significant improvement in the compressive strength and tensile strength. Thermal conductivity is analyzed for 28 d cured concrete samples using Heat flow FOX-50 instrument. Thermal conductivity reduces by 35% with the replacement of 30% sand over cenosphere which shows the significant reduction. Due to the lower density of cenosphere density of concrete samples reduced which is one of the leading factors to the lower thermal conductivity. Study concluded by replacement of 30% FA cenosphere compressive strength increased conversely thermal conductivity and density of the concrete specimen has reduced.