This research examines the mechanical characteristics of self-compacting lightweight concrete (SCLC) produced with limestone powder and reinforced by polypropylene fiber. The compressive strength, impact resistance, elastic modulus, splitting tensile strength, and flexural strength are measured at the ages of 28 days, and the toughness index of the specimens is determined from load-deflection relationships. The test results reveal that adding fiber does not affect the compressive strength, but it slightly improves the elastic modulus and the splitting tensile strength. The impact resistance and flexural properties show the most remarkable improvement; this enhancement is more superior when macro and hybrid fiber are added instead of a single microfiber with a greater improvement when the highest macro fiber content is used in the hybrid concrete specimens. (C) 2020 Elsevier Ltd. All rights reserved.

In this study, self-compacting lightweight concrete (SCLC) was prepared using crushed limestone dust, and the effects of different types of polypropylene fibers and chemical admixtures on the rheological properties of SCLC were investigated. The workability of SCLC was assessed by conducting slump flow, J-Ring, and V-funnel tests, and the compressive strength of the cubic specimens was measured at the ages of 2, 7, and 28 days. Overall, specimens containing fibers displayed lower workability than the control mix; however, a simple adjustment of the dosages of the superplasticizer and viscosity-modifying admixture remedied this problem. The results reveal that the maximum fiber content is 4 kg/m(3) for microfibers and 6 kg/m(3) for macrofibers. Producing SCLC containing 33% limestone powder by weight as cementitious material satisfied self-compacting concrete requirements and exhibited compressive strength greater than 55 MPa at the age of 28 days.

In this study fiber reinforced self-compacting lightweight concrete prepared using polypropylene fiber, limestone dust, and lightweight expanded clay aggregate LECA. The workability of FRSCLC was evaluated using the slump flow test (with and without J-Ring), flow time (T500) with and V-funnel tests both immediate test and at time of 5 minutes. The compressive strength of cubic specimens measured at ages of 2, 7, and 28 days. Then a concrete block was designed and manufactured with expanded polystyrene block EPS100 as a core material. The test results showed successful floating concrete blocks produced with fiber reinforced self-compacting lightweight structural concrete

The results of 5 months of research in the topic Concrete produced with 100% recycled aggregates are presented. We worked with a mixed type recycled material from Madrid, Spain and the tests were carried out in the laboratory (OBP) of the University of Applied Sciences of Karlsruhe, Germany. The recycled material was characterized and separated into three fractions for use as aggregates in the production of concretes (i) fine fraction 0–4 mm (ii) intermediate fraction 4–9 mm (iii) coarse fraction of 9–16 mm. To improve the properties of the recycled aggregates, different treatments were used for each of the fractions (i) accelerated carbonation of the fine fraction, (ii) encapsulation of the intermediate fraction with steam curing, (iii) use of MSC, in this case an active mineral addition of calcined clay-limestone base, denominated by its acronym in English LC2. Established as state parameters for accelerated carbonation of the fine fraction Relative Humidity = 75%, CO2 concentration = 20% and residence time of 24 h, which resulted in an increase of 0.7% in the formation of Calcite with respect to the fine fraction without carbonation, the absorption of water decreased by 0.63% and the resistance in mortars after 28 days of curing exceeded by 0.89% the strength of the fraction without carbonation, 28 Mpa and 31, 43 Mpa respectively. For the steam curing of the encapsulated fraction, it was worked under conditions of temperature lower than 60 °C and a residence time of 30 min, obtaining a decrease of 0.75% in the absorption of water with respect to the material without encapsulating. In the concretes produced with the treated aggregates, the best performance series was that which uses a combination of fine carbonated aggregate, encapsulated intermediate aggregate with steam curing and Portland cement 32.5 Mpa.

The substitution of natural resources by the use of recycled aggregates from construction and demolition waste is a huge advantage for the sustainability in the concrete production. The presented paper considers different processing methods of recycling material evaluated with respect to their advantages and disadvantages in sustainability. But once the recycled aggregates are used in concrete, there is a lag of knowledge in the field of its durability behavior. Durability results from a long-time study on 100% recycled aggregate concretes (RAC) suspended the real conditions in a tropical island are presented with respect to their chloride ingress. As reference a natural aggregate concrete (NAC) with the same w/c-ratio was used. The compressive strength of the RAC reached 30 MPa and is only 6% less than that for natural concrete. Samples of each concrete are exposed to three sites of different aggressiveness depending on the distance to the sea, which involves for one site wet-dry cycles by tides or changes in the relative humidity and the chloride content of the ambience. After 5 month exposure the chloride ingress of samples exposed to the sea shore is up to 39% lower in RAC than in NAC. The changes of chloride ingress with time are observed with a second measurement after 17 month exposure. Results in the carbonation show similar trends in the durability behavior with a lower carbonation depth in RAC. However, remaining tests such as electrical resistance and air permeability show better results for NAC.

Recycled aggregates from mixed recycled wastes have a high content of particles with size under 63 µm. This material is generally considered undesirable, since it increases water demand. However, these fines could fill out gaps between cement grains and increase packing density. The present work assesses the influence of fines under 63 µm on mortar and concrete made with mixed recycled aggregates. Pozzolanic activity of the powder, measured by isothermal calorimetry proves to be very low, so the material acts basically as a filler. Mortars with 6% of this fine material have a higher water demand, and thus a reduced compressive strength. However, the fine material contributes to decrease the effective porosity and increases the density of the matrix. This effect could help improving durability of the cementitious matrix. Alkalis tests carried out on mortars having 6% of fines under 63 µm shows that expansion is reduced, and the probable cause is the refinement of the pore structure through the increased packing density. Observations of polished section of concrete having 6% of fines under 63 µm made with at SEM, coupled with image processing, show a densification of the ITZ around the aggregates, possibly due to the contribution of the very fine fraction to packing density. The beneficial contribution of the very fine fraction could compensate problems with rheology and mechanical properties assessed in mortars and concrete.

This paper presents an alternative to reduce porosity of coarse recycled aggregate through coating the 4–8 mm fraction with a thin layer of cement. Coating was carried out in a lab granulator. A 0.16–0.23 mm thick cement film was placed surrounding the aggregate grain. Porosity and freeze-thaw tests carried out in the coarse coated recycled aggregate show improvement due to the encapsulation. For the same water to cement ratio, the amount of superplasticizer used in concrete made with encapsulated aggregates was reduced to a half compared to the non-coated reference, while a slight increase in strength is reported. Microstructural observation of the Interfacial Transition Zone (ITZ) between paste and coarse aggregate prove that encapsulation enhances densification of the cement matrix at the ITZ, which implies a reduction on porosity and contributes to increase strength.