Use Of Fine Recycled Aggregates Research Articles

Proportioning, fresh-state properties and rheology of self-compacting concrete with fine recycled aggregates

This work studies the proportioning and the effects in fresh state rheology of the use of fine recycled aggregates (FRA) to produce self-compacting concrete (SCC). The recycled sand was incorporated in percentages of 0%, 20%, 50% and 100%. The mix proportioning was supported with tests on mortars, in which workability was measured from 10min to 90min. Once adjusted, full concrete was produced and fresh properties evaluated (empirical and rheometer tests). The most shocking result was that mixes with 50% and 100% recycled sand lost their SCC characteristics at 90min. Contrarily the mix with 20% replacement maintained suitable passing and filling ability.

Proportioning, Microstructure and Fresh Properties of Self-compacting Concrete with Recycled Sand

The use of fine recycled aggregates from recycled concrete is limited due to the high absorption of the material and the subsequent reduction in mechanical performance. At the same time, Self-Compacting Concrete (SCC) uses large amounts of fines to ensure its flowability. Therefore, this type of concrete could allow the use of fine recycled aggregates. Hence, the aim of this work is to study the proportioning and the effects in the microstructure and the fresh basic properties of the use of recycled sand to produce SCC. The concrete mixes analyzed incorporate recycled sand (in percentages of 0%, 20%, 50% and 100%) and natural coarse aggregates. The mix design used an equivalent mortar, which allowed obtaining a suitable concrete that could be at the same time comparable between different replacement ratios and usable in real-life applications. During the design of the mixes with the mortars, the workability was measured from 10 min to 90 min using mini-cone and mini-funnel tests and the suitable ones were chosen to perform self-compacting concrete. Once this was done, these mixes were produced at concrete scale, and with these, basic properties were measured. The fine recycled aggregate changes the workability and the rheology of the mortar and concrete. These differences also affect the microstructure in terms of bonding and porosity distribution. There is a severe reduction of compressive and splitting strength as a result of the use of recycled sand, and this could be linked directly to these changes of the microstructure. The recommended substitution ratio with small decrease of mechanical performance is up to 20%.

South African construction and demolition waste procedure and its sourced material effects on concrete

This paper presents the results of a study into the use of fine aggregate from construction and demolition waste (C&DW) in the South African construction industry, and the impact this has on the important fresh and hardened properties of concrete when used as partial replacement for virgin materials. The C&DW were tested at replacement levels of 0%, 25%, 50%, 75% and 100%. The recycled fine aggregate was pre-soaked to mitigate the expected effect of higher water absorption of recycled concrete aggregate (RCA). However, pre-soaking of the fines attributed to the poor performance of the fresh and hardened properties of the concrete. The pre-soaking procedure used was problematic when used with fine aggregates and caused a large amount of excess water to be added to the concrete mix as a result. This study highlights the importance of planning the demolition process of a structure to ensure that the best possible quality of RCA can be extracted. The study revealed that the use of recycled fine aggregate as a replacement of virgin materials in the manufacture of concrete has a much greater negative impact than the use of coarse recycled aggregates. In addition, the pre-soaking procedure of fine aggregates warrants special attention.

The Carbonation Depth of Fine Recycled Aggregate Concrete

This paper is focused on carbonation resistance of fine recycled aggregate (FRA) concrete. Durability of FRA concrete is connected with uncertainties and doubts. One of the most unknown aspects of FRA cocnrete is carbonation resistance. This paper presents results of carbonation depth of FRA concrete. The FRA was originated from crushed construction and demolition (C&D) waste. There were prepared a total four concrete mixture. The first mixture was reference, did not include the FRA. In other concrete mixtures, natural sand was replaced by the FRA in various replacement ratios, specifically 10%, 20% and 30%. All prepared concrete mixtures were designated with the same parameters for clear comparison. From the test results it is possible to say that the use of the FRA as partial replacement of natural sand in concrete influences carbonation resistance of concrete. The carbonation depth was higher for concrete samples with the use of FRA. However it is possible to say that according to the carbonation resistance, the FRA concrete is possible to be used in the same applications as conventional concrete but it is necessary to verify this results.

Development of the life cycle inventory of masonry mortar made of natural and recycled aggregates

The use of recycled fine aggregate from construction and demolition waste as a replacement for natural fine aggregate in the manufacture of masonry mortar represents an environmental benefit that must be quantified. The life cycle assessment is a procedure that allows to know the environmental impacts associated with a product throughout its life cycle; for that purpose, it incorporates a series of phases of which inventory analysis is one of the most important as it directly influences its overall quality. The main aim of this study has been to develop the life cycle inventory of masonry mortars made of natural fine aggregate and recycled fine aggregate in accordance with ISO 14040 and ISO 14044, and being the system subject of study from cradle to gate level, thus boundaries included the production of the mortar components (natural fine aggregate, recycled fine aggregate, filler, cement and additive) and the production of masonry mortar in mortar plant. For the inventory development, production data given by the producers, Ecoinvent v.2.2 database and Environmental Product Declaration were used as data source. According to the results obtained, thanks to this study the main inputs regarding energy and raw material consumption and the main outputs (products, coproducts, waste and emissions) have been identified and quantified, linked to the masonry mortar life cycle and found inside the system boundaries considered. In a future research, the inventory developed shall allow to assess and compare the environmental impacts related to the production of masonry mortars made of natural fine aggregate and recycled fine aggregate.

Mechanical and Thermal Properties of Brick Produced Using Recycled Fine Aggregate

Continuous reduction of construction mineral resources, such as sand and cement, which influence the increase in cost of raw materials, has stimulated initiatives to look for alternative sustainable materials. This research aims to determine the potential and feasibility use of recycled fine aggregate (RFA) generated from demolition waste rubble wall as aggregate to replace natural sand in the production of cement and sand bricks. The brick specimens are prepared by using 100% natural sand, which is then replaced by RFA at 25%, 50%, 75%, and 100% by weight of natural sand. Research parameters, such as dimension, compressive and flexural strength, density, and water absorption, are adopted to evaluate the physical and mechanical properties of the brick specimens. In addition, the thermal conductivity of the bricks composed using different RFA proportions are studied. Experimental results clearly indicate that manufacturing cement and sand brick by incorporating RFA is possible, and the effect inclusion of RFA at certain proportions causes a significant improvement in the mechanical properties of bricks. However, to obtain better mechanical strength results, RFA dosages to replace sand should reach up to 50%.

Non-Destructive Testing of Concrete with Fine Recycled Aggregate

This paper is focused on non-destructive testing of concrete containing fine recycled aggregate (FRA). FRA was obtained from demolished concrete structures and crushed in the laboratory on fraction 0 – 4 mm. There were prepared four concrete mixtures. The first concrete mixture was control, did not include FRA. In other mixtures was natural replaced natural sand by FRA. There were tested workability of fresh concrete mixture and physical properties of hardened concrete. Finally, it is possible to say that the use of FRA influences the physical properties of concrete. The physical properties of concrete are connected with the durability of concrete. Therefore, it is necessary to focus on durability testing of FRA concrete in further research.

Stress-Strain Behavior of Mortar Mixtures Containing Construction and Demolition Waste as Fine Aggregate

In this paper it was investigated how the use of recycled fine aggregate influences the stress-strain behavior of mortar mixtures with different strengths. The mix design composition of the studied mortars, expressed by mass, were 1:2:0.45, 1:4:0.68 and 1:6:1.05 (cement: sand: water/cement ratio). The substitution percentages by mass of the natural aggregate by recycled aggregate were 15, 25 and 50%. The recycled aggregate had a grain size distribution comparable to that of natural sand and was obtained by grinding the waste produced by the partial demolition of UFRJ’s University Hospital. The mortars were evaluated under uniaxial compressive strength test after 28 days of curing. The results indicated that for the two higher strength classes the substitution rates affects its mechanical response by decreasing the strength. Besides, for the lower strength class the recycled aggregate could promote an increase of strength in the case of 25% of replacement.

Performance of Concrete Made with Recycled Aggregates from Portuguese CDW Recycling Plants

The objective of this research is the production of concrete with recycled aggregates (RA) from various CDW plants around Portugal. The influence of the RA collection location and consequently of their composition on the characteristics of the concrete produced was analysed. In the mixes produced in this research RA from five plants (Valnor, Vimajas, Ambilei, Europontal and Retria) were used: in three of them coarse and fine RA were analysed and in the remaining ones only coarse RA were used. The experimental campaign comprised two tests in fresh concrete (cone of Abrams slump and density) and eight in hardened concrete (compressive strength in cubes and cylinders, splitting tensile strength, modulus of elasticity, water absorption by immersion and capillarity, carbonation and chloride penetration resistance). It was found that the use of RA causes a quality decrease in concrete. However, there was a wide results scatter according to the plant where the RAs were collected, because of the variation in composition of the RA. It was also found that the use of fine RA causes a more significant performance loss of the concrete properties analysed than the use of coarse RA.

Use of recycled fine aggregates for Control Low Strength Materials (CLSMs) production

It is known that 50% of recycled aggregate is fine aggregate, however its use is still limited. In this research work the use of recycled fine aggregates for Controlled Low Strength Materials (CLSMs) production was analysed. Self-compacting and flowable CLSM material was composed of cement, fine aggregates, water and an air-entrained admixture. Adequate mix proportions of CLSM material produced with recycled fine aggregates were validated according to the minimum requirements of ASTM and the results obtained by CLSM produced with natural fine aggregates. Bleeding and penetration resistance for fresh state and density, porosity and absorption in hardened strength of optimum mix proportions of all CLSM mixtures with recycled aggregates were also validated.

Short and long-term behavior of structural concrete with recycled concrete aggregate

Abstract Recycling concrete construction waste is a promising way towards sustainable construction. Coarse recycled concrete aggregates have been widely studied in recent years, however only few data have been reported on the use of fine recycled aggregates. Moreover, a lack of reliable data on long-term properties of recycled aggregate concrete has to be pointed out. In this paper the effects of both fine and coarse recycled concrete aggregates on short and long-term mechanical and physical properties of new structural concrete are investigated. The studied concrete mixes have been designed by adjusting and selecting the content and grain size distribution of concrete waste with the goal to obtain medium–high compressive strength with high content of recycled aggregates (ranging from 27% to 63.5% of total amount of aggregates). Time-dependent properties, such as shrinkage and creep, combined with porosity measurements and mechanical investigations are reported as fundamental features to assess structural concrete behavior.

Use of fine recycled aggregates from ceramic waste in masonry mortar manufacturing

This paper evaluates the performance of fresh and hardened masonry mortar manufactured using fine recycled aggregate from ceramic partition wall rubble. Five mortars were prepared replacing 0%, 5%, 10%, 20%, and 40% of the natural sand by fine recycled aggregate. A 1:7 volumetric cement-to-aggregate ratio was used. The data were analysed using a one-way analysis of variance and the results showed that replacement ratios of up to 40% by volume did not significantly affect the properties of fresh and hardened mortar, with the exception of density and workability. Therefore, the use of fine recycled aggregates in masonry mortar manufacturing could be a viable alternative that would help increase the recycling rate of construction and demolition waste and support sustainable development in the building sector.

Influence of CDW Recycled Aggregate on Drying Shrinkage of Mortar

The use of fine recycled aggregates as raw material in the production of mortars appears as a good alternative to minimize waste disposal, so as to reduce natural resources consumption and to find and supply suitable substitutes for natural aggregates. However, the use of this alternative material in a safe way must be carried out by a wide investigation of its long term behavior. In this way, this paper will examine the mechanical strength, physical properties and drying shrinkage of mortar, which use recycled fine aggregates that have originated from construction and demolition waste (CDW) containing mortar (55%), ceramic (26%) and concrete (16%). Two natural mortars, made with natural sand, were produced with cement/sand ratios of 1:4 and 1:8 (by weight) and a fixed consistency index of 260 +10 mm. Recycled mortar was produced with 50% of substitution rate, in volume, of natural aggregate by recycled one. Results show that recycled mortars present higher total porosity, absorption rate and drying shrinkage than reference mortar.

Use of recycled fine aggregate in concretes with durable requirements

The use of construction waste materials as aggregates for concrete production is highly attractive compared to the use of non-renewable natural resources, promoting environmental protection and allowing the development of a new raw material. Several countries have recommendations for the use of recycled coarse aggregate in structural concrete, whereas the use of the fine fraction is limited because it may produce significant changes in some properties of concrete. However, during the last decade the use of recycled fine aggregates (RFA) has achieved a great international interest, mainly because of economic implications related to the shortage of natural sands suitable for the production of concrete, besides to allow an integral use of this type of waste. In this study, the durable behaviour of structural concretes made with different percentage of RFA (0%, 20%, and 30%) is evaluated. Different properties related to the durability of concretes such as absorption, sorptivity, water penetration under pressure, and carbonation are determined. In addition, the results of compressive strength, static modulus of elasticity and drying shrinkage are presented. The obtained results indicate that the recycled concretes have a suitable resistant and durable behaviour, according to the limits indicated by different international codes for structural concrete.

The possibility use of recycled fine aggregate in production of cement and sand bricks

This research aims to study the possible use of recycled fine aggregate made from waste rubble wall. We investigated recycled fine aggregates from rubble walls collected from damaged structures. The waste underwent mechanised crushing and sieving to produce fine aggregate (below 5 mm). The brick specimens were prepared using 100% natural sand. These were then replaced by recycled fine aggregate at 25, 50, 75, and 100% vis-a-vis the weight of natural sand. A series of tests was performed to study the effect of recycled aggregate on the physical and mechanical properties of bricks. The results indicate that it is possible to manufacture bricks containing recycled fine aggregate provided that the percentage of recycled fine aggregates is limited to 50-75%. This project also demonstrates that it is feasible to use alternative construction materials to manufacture a commercial product that can compete with similar products made with standard natural aggregate.

Influence of recycled fine aggregates on the resistance of mortars to magnesium sulfate attack

The influence of recycled fine aggregates, which had been reclaimed from field-demolished concretes, on the resistance of mortar specimens to magnesium sulfate attack was investigated. Mortar specimens were prepared with recycled fine aggregates at different replacement levels (0%, 25%, 50%, 75% and 100% of natural fine aggregate by mass). The mortar specimens were exposed to 4.24% magnesium sulfate solution for about 1 year at ambient temperature, and regularly monitored for visual appearance, compressive strength loss and expansion. Additionally, in order to identify products of magnesium sulfate attack, mortar samples incorporating 0%, 25% and 100% replacement levels of the recycled fine aggregates were examined by X-ray diffraction (XRD) technique. Experimental results confirmed that the use of recycled fine aggregates up to a maximum 50% replacement level is effective under severe magnesium sulfate environment, irrespective of type of recycled fine aggregates. However, the worse performance was observed in mortar specimens incorporating 100% replacement level. It was found that the water absorption of recycled fine aggregates affected deterioration of mortar specimens, especially at a higher replacement level. XRD results indicated that the main cause of deterioration of the mortar specimens was primarily due to the formation of gypsum and thaumasite by magnesium sulfate attack. In addition, it appeared that the conversion of C-S-H into M-S-H by the attack probably influenced mechanical deterioration of mortar specimens with recycled fine aggregates.

Properties of concrete prepared with crushed fine stone, furnace bottom ash and fine recycled aggregate as fine aggregates

This paper presents the results of a study to compare the properties of concretes prepared with the use river sand, crushed fine stone (CFS), furnace bottom ash (FBA), and fine recycled aggregate (FRA) as fine aggregates. Two methods were used to design the concrete mixes: (i) fixed water–cement ratio (W/C) and (ii) fixed slump ranges. The investigation included testing of compressive strength, drying shrinkage and resistance to chloride-ion penetration of the concretes. The test results showed that, at fixed water–cement ratios, the compressive strength and the drying shrinkage decreased with the increase in the FBA content. FRA decreased the compressive strength and increased the drying shrinkage of the concrete. However, when designing the concrete mixes with a fixed slump value, at all the test ages, when FBA was used as the fine aggregates to replace natural aggregates, the concrete had higher compressive strength, lower drying shrinkage and higher resistance to the chloride-ion penetration. But the use of FRA led to a reduction in compressive strength but increase in shrinkage values. The results suggest that both FBA and FRA can be used as fine aggregates for concrete production.

Effects of Fine Recycled Aggregate as Sand Replacement in Concrete

Although fine recycled aggregate (RA) constitutes a significant amount of C&D wastes after crushing, the current specification in Hong Kong momentarily does not allow the use of fine RA in ready-mixed concrete production due to its high water absorbability, which is believed to have a negative impact on the workability and durability performances of the resulting concrete. Nevertheless, few studies have quantified the detrimental effects of fine RA on the properties of concrete. This paper, therefore, presents a research study for accessing the influences of fine RA on the properties of concrete prepared with coarse natural aggregate. In order to tackle the high water absorption of the fine RA in the mixing stage, a double mixing method was adopted in lieu of the traditional mixing method. The results indicated that the mechanical properties and some of the durability parameters were debilitated by the incorporation of the fine RA. However, these drawbacks could be adequately compensated by the use of fly...

Sulfate Attack of Mortars Containing Recycled Fine Aggregates

From both environmental and sustainability points of view, it is imperative for engineers to effectively use the increasing amounts of concrete waste available. This article reports on a study of the durability of mortar specimens made with recycled fine aggregate exposed to external sulfate attack. The replacement level and the type of the recycled fine aggregate were the primary variables. The mortar specimens were immersed in a 5% sodium sulfate solution for 360 days and regularly monitored for visual damage, variation of expansion, and compressive strength. At the end of 360 days, the products of sulfate attack and the mechanism of attack were investigated through x-ray diffraction and scanning electron microscopy. Results show that the use of recycled fine aggregates up to a maximum of 50% replacement level had a beneficial effect on durability against sulfate attack, in terms of strength loss and expansion. Mortar specimens incorporating 100% replacement level, regardless of type of recycled aggregate, suffered severe deterioration. The water absorption of the recycled fine aggregate was a major factor controlling expansion, strength loss, and the intensity of damage due to sulfate attack. The microstructural studies indicated that the primary cause of deterioration of the mortar specimens with recycled aggregate was the formation of thaumasite and gypsum due to sulfate attack. The authors hypothesize that incorporation of recycled fine aggregate possibly led to the production of a relatively weak interfacial transition zone, particularly when high replacement levels were employed. The authors conclude that, when recycled fine aggregates with high water absorption are used in concrete, the limiting level of replacement is 50%. Care in the design of concrete mixtures should be taken even when such concretes are used in normal exposure conditions.