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.
A new series of layered perovskite-like oxides Bi3−xNdxTi1.5W0.5O9 (x = 0.25, 0.5, 0.75, 1.0) was synthesized by the method of high-temperature solid-state reaction, in which partial substitution of bismuth (Bi) atoms in the dodecahedra of the perovskite layer (A-positions) by Nd atoms takes place. X-ray structural studies have shown that all compounds are single-phase and have the structure of Aurivillius phases (APs), with close parameters of orthorhombic unit cells corresponding to space group A21am. The dependences of the relative permittivity ε/ε0 and the tangent of loss tgσ at different frequencies on temperature were measured. The piezoelectric constant d33 was measured for Bi3−xNdxTi1.5W0.5O9 (x = 0.25, 0.5, 0.75) compounds of the synthesized series.
The high voltage spinel material LiMn1.5Ni0.5O4 (LMNO) has the potential to increase the energy density of lithium batteries. However, its battery performance suffers from poor long-term cycling and high-temperature stability. In order to overcome these limitations, we have studied the effect of partial substitution of Mn with Ti and LiMn1.5−x Ni0.5TixO4 (x = 0.05, 0.1, 0.3), LMNTO, materials have been synthesized in a newly modified sol-gel method and then characterized by TEM, SEM (EDX), AC Electrochemical Impedance Spectroscopy and Soft X-ray Spectromicroscopy. We have demonstrated that the long-term cycling limitation with these types of materials can be resolved and herein 2000 cycles at a high C-rate have been demonstrated in half cells. We have attributed this behavior to a possible charge compensation mechanism as evidenced by a Soft X-ray Spectromicroscopy study of delithiated LMNTO materials. This work takes high energy density batteries based on high voltage spinel material one step further towards commercialization, and it is believed that further improvement can be achieved using new electrolyte formulations.
Biomass for non-food applications is considered as a substitute for petro-based materials such as expanded polystyrene (EPS). This research analyzes physical properties of an EPS containing commercial bonded leveling compound (BLC) which was substituted with cup plant (Silphium perfoliatum L.) biomass. Cup plant is a high-yielding biomass plant with several ecological benefits that is yet mainly used for biogas production. Furthermore, the high amount of parenchyma in senescent biomass with its EPS-like structure could be a possible substitute for petrochemical foams in lightweight aggregates. The natural variation in parenchyma content of several European cup plant accessions is promising, regarding the development of cultivars with suitable biomass properties for the proposed material use. Two binders with different proportions of cup plant and EPS were used to produce samples of BLC for thermal conductivity and compression strength tests. The compression strength of 0.92 N mm−2 and a thermal conductivity of 84 mW m−1 K−1 were analyzed and comparable to the commercial BLC. The thermal conductivity within the tested borders appears nearly independent of the biomass content. With increasing cup plant content, the shape characteristics of the lightweight aggregate mix changes towards more elongated aggregates. The mechanical strength and thermal conductivity are highly sensitive to the water demand of the biomass. Direct partial substitution of EPS by cup plant appears feasible and could be a part of the decarbonization of the construction sector.
The current practice of concrete is thought to be unsuitable because it consumes large amounts of cement, sand, and aggregate, which causes depletion of natural resources. In this study, a step towards sustainable concrete was made by utilizing recycled concrete aggregate (RCA) as a coarse aggregate. However, researchers show that RCA causes a decrease in the performance of concrete due to porous nature. In this study, waste glass (WG) was used as a filler material that filled the voids between RCA to offset its negative impact on concrete performance. The substitution ratio of WG was 10, 20, or 30% by weight of cement, and RCA was 20, 40, and 60% by weight of coarse aggregate. The slump cone test was used to assess the fresh property, while compressive, split tensile, and punching strength were used to assess the mechanical performance. Test results indicated that the workability of concrete decreased with substitution of WG and RCA while mechanical performance improved up to a certain limit and then decreased due to lack of workability. Furthermore, a statical tool response surface methodology was used to predict various strength properties and optimization of RCA and WG.
Although the all-inorganic perovskite CsPbI3 exhibits superior thermal- and photo-stability compared with organic-inorganic perovskites, formation of the photoactive α-phase requires sintering at approximately 320 oC. Herein, we report the partial substitution of Ge2+ ions for Pb2+ as a means of tuning the stability of the material and enabling α-phase formation at 90 oC.
Since the building made of cement concrete consumes almost half of the total energy generated and accordingly accountable for huge amount of CO2 emission, it is necessary to replace the Portland cement (PC) with sustainable construction material. Similarly, Prosopis Juliflora is a shrub or small tree in the family Fabaceae, a kind of mesquite which is considered to be a potential threat for ground water in South India. Hence, this has to eradicate so as to maintain the groundwater and also to effectively utilize its ash thereby reducing environmental pollution, this can be used as a partial replacement for cement. In this regard, this paper investigates the technical feasibility of using Prosopis Juliflora ash (PJA) as cementitious material by partially (5%, 10% and 15%) replacing cement by Prosopis Juliflora ash. The mixes were evaluated for their fresh, physical and strength properties such as workability, density and compressive strength and the results were compared with the conventional mix. In order to save the environment and to save the resources we have come up with using the Prosopis Juliflora (Semai-Karuvelam in Tamil) ash as the partial replacement of cement. Cement will produce equal amount of greenhouse gas (co2) which increase the global warming. As the amount of cement is reduced greenhouse gases also reduced. Utilization of Juliflora ash as a partial substitution for cement is one of the promising methods to increase the strength and thermal insulation for cement blocks. The strength parameters (compressive strength, split tensile strength and flexural strength) of concrete with blended Prosopis Juliflora cement are evaluated.