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The development of a three-dimensional conductivity probe, based on the measurement of electrical conductance between electrodes, to evaluate the setting time of fresh concrete and the variation of moisture content with time in hardened... more
The development of a three-dimensional conductivity probe, based on the measurement of electrical conductance between electrodes, to evaluate the setting time of fresh concrete and the variation of moisture content with time in hardened concrete is reported. The construction and calibration of the conductivity probe are described, and a calibration curve translating electrical conductance measurements into available moisture content is presented. Tests are then reported to evaluate the setting time of fresh concrete, and these are related to internal temperature variations. These tests are then extended to study moisture variations in hardened concrete under load and no-load conditions in both sealed and unsealed environments. These measurements taken for up to two years are related to internal humidity measurements. The results show that the conductivity probe is a simple and inexpensive device that gives quantitative information in any direction and possesses qualities of accuracy, reliability, long-term stability, and local resolution.
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Incorporating expanded polystyrene granules in a concrete matrix can produce lightweight polystyrene aggregate concrete of various densities. This paper examines the suitability of the DIN 1048: Compaction Index test to the polystyrene... more
Incorporating expanded polystyrene granules in a concrete matrix can produce lightweight polystyrene aggregate concrete of various densities. This paper examines the suitability of the DIN 1048: Compaction Index test to the polystyrene aggregate concrete having the unit weight of 1600, 1800 and 2000 kg/m, with the cement contents of 350, 420, 490, and 560 kg/m . A comparison is made between the compaction index and slump. It was found that workability of polystyrene aggregate concrete could be classified in terms of the compaction index. The compaction index ranges are 1.03 to 1.13, 1.14 to 1.29, 1.30 to 1.40, and 1.41 to 1.52 for high, medium, low and very low degrees of workability, respectively. For a given workability, the slump of concrete is significantly affected by its unit weight.
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A graphene oxide-modified pervious concrete was developed by using low-reactivity, high-calcium fly ash as sole binder and chemical activators and other admixtures. The density, void ratio, mechanical strength, infiltration rate, Young’s... more
A graphene oxide-modified pervious concrete was developed by using low-reactivity, high-calcium fly ash as sole binder and chemical activators and other admixtures. The density, void ratio, mechanical strength, infiltration rate, Young’s modulus, freeze-deicer salt scaling, and degradation resistance of this pervious concrete were measured against three control groups. The test results indicate that graphene oxide modified fly ash pervious concrete is comparable to Portland cement pervious concrete. While the addition of 0.03% graphene oxide (by weight of fly ash) noticeably increased the compressive strength, split tensile strength, Young’s modulus, freeze-deicer salt scaling, and degradation resistance of fly ash pervious concrete, it reduced the void ratio and infiltration rate. The fly ash pervious concrete also showed unfavorable high initial loss during the freeze-deicer salt scaling test, which may be attributed to the low hydration degree of fly ash at early age. It is recom...
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This paper reports the results of an experimental study into the effects of incorporating expanded polystyrene beads in concrete on the temperature development in an insulated thick concrete section. A varying amount of non-heat... more
This paper reports the results of an experimental study into the effects of incorporating expanded polystyrene beads in concrete on the temperature development in an insulated thick concrete section. A varying amount of non-heat conducting expanded polystyrene beads by partially replacing the normal weight aggregates to obtain the unit weights of 2215, 2100, and 1835 kg/m 3 . Cement content and water to cement ratio for the mixtures were kept constant at 500 kg/m 3 and 0.30, respectively. The concrete mixture with the largest amount of polystyrene beads produced a peak temperature of 85.6 o C compared to 70.6 o C for the
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Waste concrete produced from demolition of concrete structures is an alternative source for the production of concrete aggregates and acceptance of recycled concrete aggregates for the production of new concrete depends on the quality of... more
Waste concrete produced from demolition of concrete structures is an alternative source for the production of concrete aggregates and acceptance of recycled concrete aggregates for the production of new concrete depends on the quality of them. This paper discusses results of a series of investigations into the properties of recycled concrete aggregates and the effects of using them on the properties of concrete. Concrete aggregates differ from the natural aggregates due to the presence of a considerable proportion of mortar attached to the natural aggregates and consequently affecting the properties and performance of concrete. The results show that for recycled aggregate concrete, compressive and tensile strengths and modulus are reduced, whereas drying shrinkage and creep are increased. The effect of using concrete fine aggregate on the modulus and shrinkage is less than those produced by the use of concrete coarse aggregate. The strength of recycled aggregate concrete can be reco...
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This paper reports on the data of setting time, strength, modulus of elasticity, drying shrinkage, and compressive creep of concrete containing a low-calcium fly ash under hot and humid (28 n 2 C, 75 n 15 percent, relative humidity)... more
This paper reports on the data of setting time, strength, modulus of elasticity, drying shrinkage, and compressive creep of concrete containing a low-calcium fly ash under hot and humid (28 n 2 C, 75 n 15 percent, relative humidity) climate. Tests were carried out for Grade 25 and 35 concretes. The cement replacements with fly ash were 0, 20, and 40 percent, by weight. Between 3 and 90 days under moist curing (28 n 1 C), fly ash concrete gives rise to strength increases of about 110 and 230 percent with the fly ash contents of 20 and 40 percent, respectively, compared to an increase of about 65 percent for the control concrete. The relationship between the modulus of elasticity and compressive strength was not influenced by the partial replacement of cement by fly ash. Both grades of concrete with 40 percent fly ash content and moist cured initially for 7 days showed about 35 percent more drying shrinkage after 90 days of drying than the corresponding shrinkage for the control concr...
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Lightweight expanded polystyrene, a well known material to absorb impact energy, is being used to produce adjusted density concrete having enhanced impact energy absorption capacity concrete. Two structural concrete grades, 30 and 45 MPa,... more
Lightweight expanded polystyrene, a well known material to absorb impact energy, is being used to produce adjusted density concrete having enhanced impact energy absorption capacity concrete. Two structural concrete grades, 30 and 45 MPa, normal weight concrete and lightweight polystyrene concrete were tested for their impact response under 75kg weight test through 462mm drop. The impact response of concrete was monitored through load-time plot. Peak load and contact time are considered as important measurable quantities in identifying the energy absorbing capacity of concrete. The results showed that for a given structural grade the concrete containing expanded polystyrene aggregate out-performed the normal weight concrete in its impact resistance. Under the tested impact loading condition, polystyrene concrete having the compressive strength of 30MPa showed 28% increase in the contact time and 18% reduction in the peak load compared to the similar grade normal weight concrete.
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A statistical analysis was made using the results of experimental factorial design about the volume of permeable voids (VPV) of recycled aggregate concrete samples using the proceedings of ASTM C 642-97. The recycled aggregates were made... more
A statistical analysis was made using the results of experimental factorial design about the volume of permeable voids (VPV) of recycled aggregate concrete samples using the proceedings of ASTM C 642-97. The recycled aggregates were made from crushed and sieved concrete, mortar and red ceramic. The proposed model shows that the VPV increased for all recycled concrete samples and the recycled red ceramic coarse aggregate is the most influential and the recycled mortar fine aggregate is the lesser one.
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This paper reports on the data of setting time, strength, modulus of elasticity, drying shrinkage, and compressive creep of concrete containing a low-calcium fly ash under hot and humid (28 n 2 C, 75 n 15 percent, relative humidity)... more
This paper reports on the data of setting time, strength, modulus of elasticity, drying shrinkage, and compressive creep of concrete containing a low-calcium fly ash under hot and humid (28 n 2 C, 75 n 15 percent, relative humidity) climate. Tests were carried out for Grade 25 and 35 concretes. The cement replacements with fly ash were 0, 20, and 40 percent, by weight. Between 3 and 90 days under moist curing (28 n 1 C), fly ash concrete gives rise to strength increases of about 110 and 230 percent with the fly ash contents of 20 and 40 percent, respectively, compared to an increase of about 65 percent for the control concrete. The relationship between the modulus of elasticity and compressive strength was not influenced by the partial replacement of cement by fly ash. Both grades of concrete with 40 percent fly ash content and moist cured initially for 7 days showed about 35 percent more drying shrinkage after 90 days of drying than the corresponding shrinkage for the control concrete. However, the shrinkage was found to be about 7 percent lower than that for the control concrete when the initial moist curing period was increased from 7 to 28 days. For Grade 35 concrete, the creep coefficient of concrete with fly ash content of 40 percent was 11 percent lower than that of the control concrete. However, Grade 25 concrete showed a 4 percent higher creep coefficient for fly ash concrete with the same 40 percent fly ash content.
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Coarse and fine aggregates generated from crushed concrete products for new concrete can be generally accepted only when the properties of recycled aggregate concrete, in addition to the relationships between different properties of such... more
Coarse and fine aggregates generated from crushed concrete products for new concrete can be generally accepted only when the properties of recycled aggregate concrete, in addition to the relationships between different properties of such a concrete, are well understood. ...
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... Ahead of print articles are fully citable using the DOI number and accessible using the link below. More like this? In this publication; By this author: R. Sri Ravindrarajah , YH Loo , CT Tam. Synopsis. The effects of using crushed ...
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ABSTRACT Increasing shortage of natural aggregates for concrete in urban areas leads to a search for aggregates from new sources. This paper examines the use of crushed concrete fines (CCF) produced from ‘waste’ concrete as fine aggregate... more
ABSTRACT Increasing shortage of natural aggregates for concrete in urban areas leads to a search for aggregates from new sources. This paper examines the use of crushed concrete fines (CCF) produced from ‘waste’ concrete as fine aggregate in concrete. Tests were carried out to study the properties of crushed concrete fines and the properties of concrete incorporating them. The results show that the modulus of elasticity, pulse velocity, and the long-term properties such as drying shrinkage and creep are significantly affected. It has been found that the detrimental effects of using crushed concrete fines in concrete can be mitigated by a partial replacement of crushed concrete fines with pulverised fuel ash (pfa).
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Concrete for sustainable infrastructure construction of civil engineering structures is required to use environmentally friendly concrete-making materials and to minimize both energy and manpower needs in concrete placing. With the... more
Concrete for sustainable infrastructure construction of civil engineering structures is required to use environmentally friendly concrete-making materials and to minimize both energy and manpower needs in concrete placing. With the intension of improving both environmental and economical sustainability, this study on self-compacting concrete with ground granulated blast furnace slag and recycled concrete aggregate was conducted. This paper reports the results of an experimental investigation into the production and proper-ties of high-strength self-compacting concrete mixes with a combination of Portland cement and ultra-fine slag (up to 50% of cement replacement) and with either natural or recycled concrete coarse aggregate. The strengths development and chloride migration coefficient was evaluated. The use of ultra-fine slag was found to improve the stability of self-compacting concrete independent of the type of coarse aggregate. The use of recycled concrete decreased the strengths and modulus of elasticity and increased the chloride permeability for the high strength self-compacting concrete.
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"The development of a three-dimensional conductivity probe, based on the measurement of electrical conductance between electrodes, to evaluate the setting time of fresh concrete and the variation of moisture content with... more
"The development of a three-dimensional conductivity probe, based on the measurement of electrical conductance between electrodes, to evaluate the setting time of fresh concrete and the variation of moisture content with time in hardened concrete is reported. The construction and calibration of the conductivity probe are described, and a calibration curve translating electrical conductance measurements into available moisture content is presented. Tests are then reported to evaluate the setting time of fresh concrete, and these are related to internal temperature variations. These tests are then extended to study moisture variations in hardened concrete under load and no-load conditions in both sealed and unsealed environments. These measurements taken for up to two years are related to internal humidity measurements. The results show that the conductivity probe is a simple and inexpensive device that gives quantitative information in any direction and possesses qualities of accuracy, reliability, long-term stability, and local resolution."
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Construction and Demolition (C&D) waste is an important portion of solid waste produced in Brazilian cities, corresponding around 50% of urban solid wastes. Among several representatives of C&D waste, red ceramic, originated from bricks... more
Construction and Demolition (C&D) waste is an important portion of solid waste produced in Brazilian cities, corresponding around 50% of urban solid wastes. Among several representatives of C&D waste, red ceramic, originated from bricks and tiles used in constructions, is a considerable portion. The recycling of C&D waste making recycled aggregates has been a common practice, particularly in cities where there is an inaccessibility or shortage of natural aggregates, that propitiate high costs to acquire them. Intending determine the behavior of red ceramic recycled aggregates in concrete's production, it was made an experimental program based on a project of experiments. In this program, the fine and the coarse natural aggregates were substituted by theirs respective recycled aggregates. The water/cement ratio was also varied. The produced concretes were analyzed regarding three properties: axial strength, modulus of deformation and volume of permeable voids (VPP). All the propo...
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ABSTRACT
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Os resíduos de construção e demolição (RCD) constituem uma importante parcela dos resíduos sólidos produzidos nas cidades brasileiras, correspondendo em torno de 50% dos resíduos sólidos urbanos. Dentre os diversos constituintes do RCD, a... more
Os resíduos de construção e demolição (RCD) constituem uma importante parcela dos resíduos sólidos produzidos nas cidades brasileiras, correspondendo em torno de 50% dos resíduos sólidos urbanos. Dentre os diversos constituintes do RCD, a cerâmica vermelha, proveniente de restos de tijolos e telhas cerâmicas utilizados nas construções, equivale a uma considerável parcela destes resíduos. A reciclagem do RCD para a produção de agregados reciclados tem se tornado uma prática cada vez mais comum, particularmente em cidades onde há uma inacessibilidade ou escassez de agregados naturais, proporcionando altos custos para adquiri-los. Com o intuito de se determinar o comportamento do agregado reciclado de cerâmica vermelha na produção de concretos, desenvolveu-se um programa experimental baseado em um projeto de experimentos onde se substituiu os agregados miúdos e graúdos naturais pelos seus respectivos reciclados, além de se variar a relação água/cimento. Os concretos produzidos foram an...
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Pervious concrete, a tailored concrete with connected large-sized voids, allows the water to flow through easily. In-situ pervious concrete pavements is produced with no or minimum compaction with fairly dry but workable concrete mix.... more
Pervious concrete, a tailored concrete with connected large-sized voids, allows the water to flow through easily. In-situ pervious concrete pavements is produced with no or minimum compaction with fairly dry but workable concrete mix. This construction method contributes to variable permeability and strength performance within the pervious concrete pavements. In order to improve the reliability of pervious concrete pavements the use of precast pervious pavers produced with strict quality control is a possible solution. This paper reports the results of an investigation into the performance of 300 mm by 300 mm by 75 mm matured laboratory made pervious concrete pavers, in relation to overall water permeability, variability of water permeability within each paver and rate of drying of saturated pavers at 20◦C, 30◦C and 40◦C. The void content of the twelve precast pavers used in this study is varied between 12% and 22%. The results showed: (a) the existence of non-uniformity of water permeability within a pervious concrete paver independent of its porosity; (b) an increase in the thickness of the pervious concrete paver decreased the water infiltration rate; (c) with the decrease in the void content the overall permeability of the pervious concrete pavers is decreased; (d) the drying rate of pervious slabs is increased with the increase in temperature; (e) the influence of void content on dry rate is reduced with the increase in the drying temperature.
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... than the original crushed granite aggregate. The resistance to mechanical actions such as impact, crushing and abrasion for the recycled concrete aggregates is also lower. The effects of using recycled concrete aggregates ...
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... Authors: CT Tam; TY Lim; R. Sri Ravindrarajah; SL Lee; Source: Magazine of Concrete Research, Volume 39, Issue 138, pages 12 18 , ISSN : 0024 ... The journal also publishes articles ahead of print to ensure you receive access to the... more
... Authors: CT Tam; TY Lim; R. Sri Ravindrarajah; SL Lee; Source: Magazine of Concrete Research, Volume 39, Issue 138, pages 12 18 , ISSN : 0024 ... The journal also publishes articles ahead of print to ensure you receive access to the latest research as soon as it is published. ...
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... material3 for a pavement, as the material of construction for floating marine structures ... the results of an investigation into the properties of polystyrene aggregate concrete with this ... EXPERIMENTAL INVESTIGATION Materials Type... more
... material3 for a pavement, as the material of construction for floating marine structures ... the results of an investigation into the properties of polystyrene aggregate concrete with this ... EXPERIMENTAL INVESTIGATION Materials Type GP Portland cement, conforming to AS 3972, and ...