scholarly journals Rheology of Alkali-Activated Mortars: Influence of Particle Size and Nature of Aggregates

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 726
Author(s):  
Sara Gismera ◽  
María del Mar Alonso ◽  
Marta Palacios ◽  
Francisca Puertas
Keyword(s):  
Particle Size ◽  
Aggregate Size ◽  
Recycled Concrete ◽  
Partial Replacement ◽  
Rheological Parameters ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
General Terms ◽  
Dynamic Yield ◽  
Alkali Activated

The effect of two precursors (slag and fly ash), different particle size distribution, and three types of aggregate (siliceous sand, limestone, and recycled concrete) on alkali-activated material (AAM) mortar rheology were studied and compared to their effect on an ordinary Portland Cement (OPC) mortar reference. Stress growth and flow curve tests were conducted to determine plastic viscosity and static and dynamic yield stress of the AAM and OPC mortars. In both OPC and AAM mortars, a reduction of the aggregate size induces a rise of the liquid demand to preserve the plastic consistency of the mortar. In general terms, an increase of the particle size of the siliceous aggregates leads to a decrease of the measured rheological parameters. The AAM mortars require higher liquid/solid ratios than OPC mortars to attain plastic consistency. AAM mortars proved to be more sensitive than OPC mortars to changes in aggregate nature. The partial replacement of the siliceous aggregates with up to 20% of recycled concrete aggregates induced no change in mixing liquid uptake, in either AAM or OPC mortars. All the AAM and OPC mortars studied fitted to the Bingham model.

scholarly journals Physical Characterization of Dutch Fine Recycled Concrete Aggregates: A Comparative Study

Proceedings ◽  
2019 ◽  
Vol 34 (1) ◽  
pp. 7 ◽  
Author(s):  
Marija Nedeljković ◽  
Jeanette Visser ◽  
Siska Valcke ◽  
Erik Schlangen
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Water Absorption ◽  
Size Distribution ◽  
Surface Area ◽  
Recycled Concrete ◽  
Natural Sand ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates

In the Netherlands, yearly 20 Mt Construction- and Demolition waste (CDW) is being produced mainly consisting of concrete and masonry rubble. This is two third of the yearly production of concrete (33 Mt). Currently, less than 1 Mt/year of the 20 Mt/year CDW is recycled in new concrete (mainly as coarse recycled concrete aggregates). This preliminary study being part of a larger study, is aiming to increase that amount, amongst others by focusing on use of the fine recycled concrete aggregates. Fine recycled concrete aggregates (fRCA) appear promising for (partial) replacement of natural fine aggregates (sand) and cement in new concrete. Nevertheless, they can be expected to have adverse properties and components that may reduce the performance of the concrete. Their physical, chemical and mechanical properties, which thus may significantly differ from that of natural sand, are still far from being fully investigated. The present paper focusses on characterization of physical properties of fRCA for finding the most critical indicators for fRCA quality. The tests include particle size distribution, morphology, BET surface area, solid density and water absorption of individual and total fractions (0–0.25 mm, 0.25–4 mm and 0–4 mm). The tests are performed on three fRCAs with different origin. Natural river sand with 96 wt.% of SiO2 was also studied to provide a baseline for comparison. Experimental results showed that, on the one side, the particle size distribution, surface area and amounts of individual fractions of fRCAs are significantly different from that of natural sand and that there is a large difference between each other. This is caused by variations of the parent concrete properties and by the type of recycling technique and processes (one step or multiple steps crushing). On the other side, fRCAs have comparative solid densities, which were still lower than that of natural sand. It was also shown that difference in water absorption between fractions 0.25–4 mm and 0–4 mm is very small in all three fRCAs groups. The results of this study will be used for future correlations between investigated properties of fRCAs with properties of concretes with fRCAs. This will be investigated in the next stage of the project, such that these correlations can enable production of durable concretes with fRCAs and assist recyclers in optimization of their production processes based on quality control of fRCAs.

scholarly journals Performance of Steel Fiber-Reinforced Alkali-Activated Slag-Fly Ash Blended Concrete Incorporating Recycled Concrete Aggregates and Dune Sand

Buildings ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 327
Author(s):  
Hilal El-Hassan ◽  
Abdalla Hussein ◽  
Jamal Medljy ◽  
Tamer El-Maaddawy
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Steel Fiber ◽  
Recycled Concrete ◽  
Steel Fibers ◽  
Dune Sand ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Activated Slag ◽  
Alkali Activated

This study evaluates the performance of alkali-activated slag-fly ash blended concrete made with recycled concrete aggregates (RCA) and reinforced with steel fibers. Two blends of concrete with ground granulated blast furnace slag-to-fly ash ratios of 3:1 and 1:1 were used. Natural aggregates were substituted with RCA, while macro steel fibers with 35 mm of length and aspect ratio of 65 were incorporated in RCA-based mixtures at various volume fractions. Fine aggregates were in the form of desert dune sand. Mechanical and durability characteristics were investigated. Experimental results revealed that RCA replacement decreased the compressive strength of plain concrete mixtures with more pronounced reductions being perceived at higher replacement percentages. Mixtures made with 30%, 70%, and 100% RCA could be produced with limited loss in the design compressive strength upon incorporating 1%, 2%, and 2% steel fibers, by volume, respectively. In turn, splitting tensile strength was comparable to the NA-based control while adding at least 1% steel fiber, by volume. Moreover, higher water absorption and capillary sorptivity and lower ultrasonic pulse velocity, bulk resistivity, and abrasion resistance were reported during RCA replacement. Meanwhile, incorporation of steel fibers densified the concrete and enhanced its resistance to abrasive forces, water permeation, and water transport. Analytical regression models were developed to correlate hardened concrete properties to the 28-day cylinder compressive strength.

scholarly journals Eksperimental Perbandingan Kekuatan Tekan Karakteristik Beton Self Compacting Menggunakan Agregat Kasar Alami Dan Agregat Kasar Daur Ulang

2020 ◽  
Vol 19 (1) ◽  
pp. 107-120
Author(s):  
Martinus Pramanata Sapeai ◽  
Johannes Adhijoso Tjondro
Keyword(s):  
Compressive Strength ◽  
Aggregate Size ◽  
Recycled Concrete ◽  
Mix Design ◽  
Sustainable Construction ◽  
Maximum Aggregate Size ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Coarse Aggregates ◽  
High Rise

Utilization of recycled concrete waste as an alternative to natural coarse aggregates in this experiment is in accordance with the concept of sustainable construction. Concrete is the main material of structural elements most commonly used in general construction and has properties that are difficult to recycle by themselves naturally. Nowdays concrete innovation with the concept of self compacting (SCC) is widely used especially in high rise building and buildings with special specification. SCC has high flowability properties so that it can flow and compact themselves, but in SCC with normal quality still need compactor. The concept of making test specimens is in accordance with real conditions in the field, where aggregates do not go through a cleaning process. There are four different mix design with the required specified compressive strength of 20 MPa. Mix design 1A (natural coarse) and 1B (recycled coarse aggregates) has a maximum aggregate size 12.50 mm, and mix design 2A (natural coarse) and 2B (recycled coarse aggregates) has a maximum aggregate size 19.00 mm. This experimental results in specified compressive strength concrete for mix design 1A, 1B, 2A, and 2B as follows: 30.93 MPa, 26.21 MPa, 30.82 MPa and 27.60 MPa. Therefore, recycled concrete aggregates can be alternative to natural coarse aggregates and can also be made into concrete with the SCC concept.

scholarly journals Properties of Steel Fiber-Reinforced Alkali-Activated Slag Concrete Made with Recycled Concrete Aggregates and Dune Sand

2021 ◽  
Vol 13 (14) ◽  
pp. 8017
Author(s):  
Hilal El-Hassan ◽  
Jamal Medljy ◽  
Tamer El-Maaddawy
Keyword(s):  
Compressive Strength ◽  
Steel Fiber ◽  
Recycled Concrete ◽  
Steel Fibers ◽  
Dune Sand ◽  
Alkali Activated Slag ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Activated Slag ◽  
Alkali Activated

Reutilizing industrial by-products and recycled concrete aggregates (RCA) to replace cement and natural aggregates (NA) in concrete is becoming increasingly important for sustainable development. Yet, experimental evidence is needed prior to the widespread use of this sustainable concrete by the construction industry. This study examines the performance of alkali-activated slag concrete made with RCA and reinforced with steel fibers. Natural coarse aggregates were replaced with RCA. Steel fibers were added to mixes incorporating RCA at different volume fractions. Desert dune sand was used as fine aggregate. The mechanical and durability properties of plain and steel fiber-reinforced concrete made with RCA were experimentally examined. The results showed that the compressive strength did not decrease in plain concrete mixes with 30 and 70% RCA replacement. However, full replacement of NA with RCA resulted in a 20% reduction in the compressive strength of the plain mix. In fact, 100% RCA mixes could only be produced with compressive strength comparable to that of an NA-based control mix in conjunction with 2% steel fiber, by volume. In turn, at least 1% steel fiber, by volume, was required to maintain comparable splitting tensile strength. Furthermore, RCA replacement led to higher water absorption and sorptivity and lower bulk resistivity, ultrasonic pulse velocity, and abrasion resistance. Steel fiber incorporation in RCA-based mixes densified the concrete and improved its resistance to abrasion, water permeation, and transport, thereby enhancing its mechanical properties to exceed that of the NA-based counterpart. The hardened properties were correlated to 28-day cylinder compressive strength through analytical regression models.

scholarly journals Interlocking Pavement Tiles using RCA with Industrial Waste as Admixtures

2021 ◽  
Author(s):  
Anjana S ◽  
Diya Elizabeth Isaac ◽  
Neelanjana S ◽  
Aswathy G
Keyword(s):  
Fly Ash ◽  
Industrial Waste ◽  
Recycled Concrete ◽  
Partial Replacement ◽  
Normal Concrete ◽  
Concrete Aggregates ◽  
Recycled Concrete Aggregates ◽  
Coarse Aggregates ◽  
Loss Of Strength ◽  
Enormous Quantity

The unprecedented increase in construction and developmental activities in the current era brings with it many irreversible impacts on the environment. The major impacts being the depletion of natural resources and generation of an enormous quantity of Construction and Demolition (C&D) wastes. Hence it has become important to reuse and recycle C & D wastes generated. These wastes can be processed to obtain Recycled Concrete Aggregates (RCA), which can be used for producing recycled concrete. It was found that the strength of Recycled concrete matches with that of paver quality concrete. Therefore, the study aims at producing interlocking paver blocks by replacing the normal coarse aggregates in pavers by RCA along with fly ash as admixture, an industrial waste. Fly ash being a pozzolanic admixture is used in order to overcome the loss of strength due to the addition of RCA. In the present study, a 30% replacement of normal aggregates with RCA and 15% replacement of cement with fly ash in the mix was used as it was found to provide the optimum strength. A comparison of the important properties of paver blocks were conducted between normal concrete pavers, pavers with RCA replacement and pavers with RCA replacement and fly ash. It was found out from the study that Interlocking pavers with partial replacement of normal aggregates with RCA and fly ash obtained strength comparable to that of normal paver blocks. Hence these paver blocks can be used for laying of roads and can contribute towards a sustainable development.

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