Use of Prefabrication, Construction and Demolition Wastes as an Aggregate in Vibropressed Precast Concrete Blocks Production

The aim of current study was to determine the recycled concrete aggregate (RCA) applicability in the production of concrete mixture for vibropressed concrete blocks. The experiments were focused especially on the crushed waste material from the same concrete elements producing plant. For this type of precast elements only some finer fractions can be implemented and the “earth-moist” consistency of fresh mixture is required. The series of samples was prepared in which the mixture of natural aggregates was partially or totally substituted by recycled concrete aggregate. The 0/4 RCA fraction, which is usually rejected in ready mix concrete technology, plays a role of 0/2 sand. The substitution of sand fraction was from 20% to 100% respectively. The substitution of the coarser aggregate fractions by 4/16 RCA was also done. The standard properties of vibropressed elements, such as the degree of densification, the density of material, the compressive and splitting tensile strength and the water absorption capacity according to the relevant standards were determined. The parameters of materials with the natural aggregate substitution by RCA are affected by the ratio of recycled concrete aggregate. In most cases the results do not decline specially from those for reference samples, when only the natural sand (0/2) fraction is substituted by the 0/4 recycled aggregate. As one could expect, as lower the substitution, as better the test results. The partial substitution of natural aggregate by coarser fractions requires experimental verification; over 20% substitution of natural aggregate by 4/8, 8/16 or 0/16 RCA should be excluded.

Study on Mechanical and Shrinkage Properties of High Belite Sulphoaluminate Cement-Based Green Recycled Aggregate Concrete

Green recycled aggregate concrete (RAC) with high strength and low shrinkage is prepared based on recycled coarse aggregate produced by the particle-shaping and aggregate-strengthening method and green low-carbon new cement. This not only effectively alleviates the shortage of natural resources, but also improves the performance of recycled aggregate concrete, which is of great significance for multi-channel resource utilization of construction waste. In this study, three kinds of recycled coarse aggregates (RCA), including simple crushing recycled coarse aggregate (JD-RCA), one-time particle-shaping recycled coarse aggregate (KL-RCA) and two-time particle-shaping recycled coarse aggregate (EKL-RCA), were prepared from the preparation technology of recycled aggregate, and high belite sulphoaluminate cement with excellent performance was used. The effects of aggregate quality, aggregate replacement ratio, and cementitious material content on mechanical properties and shrinkage properties of green recycled aggregate concrete were studied in comparison with ordinary Portland cement-based recycled aggregate concrete. The testing results show that the particle-shaping method can effectively improve the aggregate quality. The compressive strength and dry shrinkage performance of recycled aggregate concrete made of particle-shaped aggregate are only a little different from those of natural aggregate concrete, and even the performance of recycled aggregate is better than that of natural aggregate concrete under the condition of a low replacement ratio of recycled aggregate. In addition, high belite sulphoaluminate cement-based recycled aggregate concrete (HBRAC) not only has early strength and rapid hardening, but also has excellent drying shrinkage resistance, and its shrinkage rate can be reduced to more than 75% compared with ordinary Portland cement-based recycled aggregate concrete (OPRAC).

Fungicidal effects on cement composites with recycled glass from photovoltaic panels

This research was focused on the effects of micromycetes on cement composites with 100% replacement of natural aggregate by the recycled glass from photovoltaic panels. The experiment was performed on samples of small beams measuring 40 x 40 x 8 mm (length x width x height) and cement crumbling with recycled glass from photovoltaic panels in percentages representing 10%, 20% and 40%. The representatives of the selected micromycetes were Aspergillus niger, A. clavatus, Penicillium glabrum, Cladosporium sp. and Zygomycetes sp. Biocorrosion causes changes in the properties of the material, mainly as a result of the action of microorganisms. Due to their large production of acids and enzymes, micromycetes are an important part of microscopic consortia involved in biocorrosion. This experiment focused on evaluating the effect of micromycetes on cement composites – solid structure and crumbling, with 100% replacement of natural aggregate with photovoltaic glass recyclate. The results show a high growth of biomass on solid composites, while on cement crumbling, the growth was minimal due to high pH value. Longer monitoring time was used in case of adaptation to the environment.

Surface treatments of recycled brick aggregate and their influence on selected properties of concrete

The paper is devoted to surface treatment of recycled brick aggregate with various impregnating substances in order to reduce its absorbency and verify the use of such treated recycled material as a partial replacement of natural aggregate (fraction 4/8) in concrete. Selected properties of the tested samples were monitored after 28 and 60 days of curing. The results show that the treatment of recycled bricks with water glass appears to be a less suitable alternative compared to the use of a hydrophobic solution of silanes and siloxanes.

Effects of the Variety and Content of Natural Pozzolan Coarse Aggregate on the Thermo-Mechanical Properties of Concrete

The present study investigated the effects of the variety and content of three natural pozzolan coarse aggregates on concrete. Natural pozzolan aggregates have been obtained from three volcanoes (Boutagrouine, Timahdite, and Jbel Hebri) located in the Middle Atlas region in Morocco. The three pozzolans studied were characterized, and then a comparison was made by replacing the natural aggregate with the pozzolan aggregate in the concrete in different percentages, namely 25, 50, and 100 % in volume. The results showed that the variety and content of pozzolan aggregate have a significant impact on the properties of concrete, primarily caused by the characterization of pozzolan aggregate. The density of concrete decreases with the addition of pozzolan aggregate, which decreases depending on the type of pozzolan aggregate used. The highest compressive strength was measured in the concrete specimens prepared with aggregate BP while the lowest compressive strength was noted in the concrete specimens prepared with aggregate RP. On the other hand, the substitution of NA at 100% by BP, GP, and RP aggregates leads to a decrease in the thermal conductivity of about 67%, 62%, and 55% respectively.

Preliminary Study of Recycled Aggregate Mortar for Electric Arc Furnace Dust Encapsulation

This article shows the preliminary results of a study carried out to determine the technical feasibility of encapsulating a high percentage of EAFD in cement-based mortars manufactured with the fine fraction of recycled concrete aggregates (RCA). Two families of mortars, with natural aggregate as a reference and with RCA, were studied. An incorporation rate by weight of two parts mortar to one part EAFD was tested. The mechanical strengths (compressive strength and tensile strength) before and after immersion in water, the rate of delitescence and the leaching behavior were studied. Mortars made with RCA showed similar mechanical strengths to the reference mortars made with natural aggregates; however, the incorporation of EAFD decreased the mechanical strengths. Encapsulation considerably reduced the leaching of heavy metals, although the Pb concentration remained above the hazardous waste limit. With this preliminary study, two wastes are managed together, and the results have shown that the use of RCA instead of natural aggregate is a viable alternative since it does not significantly impair the mechanical or leaching properties of the cement-based matrices used to encapsulate EAFD.

Periwinkle Shell as Mixing Ingredient in Concrete: A Review

Growing population which also pushes for rising demand for seafood results in a generation of seashells which are thrown as environmental pollution waste after the edible meat is consumed. Meanwhile, the utilisation of natural resources as mixing ingredients for the production of concrete materials continues to increase over the year. The use of periwinkle shells as mixing ingredients in concrete materials can lower the dependency on natural aggregate supply. This paper discusses the properties of periwinkle shell and method of treatment prior to their usage as a cement and coarse aggregate as well as the mechanical properties of concrete produced using this seashell waste. Overall, the replacement of periwinkle shell as cement and coarse aggregate must be integrated in a specified percentage to enhance the performance of the concrete. For cement replacement, 5% of replacement gives the highest strength, meanwhile 10% of replacement as coarse aggregate can meet the desired strength. The increase in the use of periwinkle shell quantity as cement or coarse aggregate replacement reduces concrete workaibility. The integration of periwinkle shell influences the compresssive strength of concrete. Accomplishment in replacing periwinkle shell as cement and coarse aggregate would reduce pollutiion due to shell dumping and save natural resources. However, further investigation in terms of durability properties is recommended.