Characteristics Of Lightweight Aggregate Research Articles

Microstructure, durability and surface free energy of lightweight aggregate modification of sanitary ceramic wastes and sewage sludge

The research on the durability and physical properties of lightweight aggregate (LWA) with addition of sanitary ceramic wastes and sewage sludge was presented in the paper. The following characteristics of LWA were defined: contact angle (CA), absorptivity, roughness, surface free energy (SFE) before and after the UV radiation durability test, thermal conductivity coefficient λ, compressive strength, freezing-thawing, salt resistance and others. Open porosity was examined using computed tomography, it reached 20.987 % for the ceramic waste aggregate, and 7.023 % for the reference aggregate. The aggregate with the largest amount of ceramic waste (20 %) and sewage sludge (10 %) has the highest average roughness (Ra), which is 14 % higher than the Ra of the reference aggregate. The contact angle decreased by almost 4 times and samples had higher absorptivity (19.994 %) when 10 % sewage sludge and 20 % sanitary ceramic were added to the aggregate. The sanitary ceramic waste application may enhance the poor durability characteristics of lightweight aggregate with/without sewage sludge. Replacing natural loess with sanitary ceramic waste material brings benefits both in terms of respect for natural resources and also improves the properties of lightweight aggregates.

Potential use of foam in the production of lightweight aggregate (LWA) and its performance in foamed concrete

This paper discusses about the production and characteristic of lightweight bubble aggregate and foamed concrete. Lightweight aggregates (LWA) are produced by mixing an appropriate amount of foam and ordinary Portland cement and pelletized into assigned size and shape. Then, the characteristics of LWA are identified to ensure that aggregate produced can be categorized into LWA with acceptable qualities. For the foamed concrete, its performances are tested and studied by selecting five different percentages for partial substitution of LWA as coarse aggregate. Main aim of the research is to identify the characteristic of lightweight foamed concrete such as density, water absorption, aggregate impact value (AIV), compressive strength after using LWA as an alternative material for construction industry. This aim also in parallel to main idea of reducing the usage of natural coarse aggregate which is granite that is facing serious depletion. Three different percentages of concrete mixtures using LWA have been prepared that consist of 25% and 50% of LWA together with control sample that contained 100% natural coarse aggregate. These three different mixes are produced manually where the mortars, foam, granite and LWA were mixed together in mixer. The samples have undergone several testing including density test, water absorption test and compression test. Microstructure of the samples also was examined using SEM. From the results obtained, foamed concrete that were produced with 25% substitution of LWA showed the highest compressive strength of 10.74 MPa with density of 1735 kg/m3. In conclusion, LWA have shown promising potential to be used in the foamed concrete production.

Effect of SiO2, Al2O3 and CaO on characteristics of lightweight aggregates produced from MSWI bottom ash sludge (MSWI-BAS)

For the utilization of municipal solid waste incineration bottom ash sludge (MSWI-BAS), the production of lightweight aggregates (LWA) was carried out using it as raw materials. SiO2, Al2O3 and CaO were the major oxides in MSWI-BAS, so their effect on characteristics of LWA was investigated to optimize the process. Results showed that the increase in SiO2 content from 25% to 40% caused the good growth of the structure with Si and O as the skeleton, leading to LWA with increased compressive strength and particle density from 0.5 to 6.18 MPa and from 755 to 1268 kg/m3 respectively, and reduced 1 h water absorption from 50% to 14%. Lower strength LWA with more pores and amorphous phases were obtained at 20% ≤ Al2O3 ≤ 30% because excessive Al2O3 inhibited the crystallization inside the products. Dramatic changes occurred when CaO increased from 21% to 22% with compressive strength and particle density from 8.82 to 2.02 MPa and from 1300 to 862 kg/m3 respectively, and 1 h water absorption from 4% to 36%, indicating that more CO2 was produced. This attempt to utilize MSWI-BAS can produce high-performance LWA that meets the sustainability philosophy and reduces the cost of waste treatment and lightweight aggregates production.

Performance and Microstructural Analysis of Lightweight Concrete Blended with Nanosilica under Sulfate Attack

The influence of two lightweight aggregates (LWA) on concrete and the effects of cement substitution for nanosilica (NS) on the interfacial transition zone (ITZ) and cementitious matrix of concrete in resistance to attacks by magnesium sulfate (MgSO4) are researched in this work. The aggregates evaluated were perlite, which is a lightweight aggregate of open porous structure, and expanded clay (aliven) with closed porous structure. The variables included in the study were replacement percentage of coarse aggregates by lightweight coarse aggregates (0 and 100% by volume) and replacement percentage of cement by nanosilica (0 and 10% by weight). In the dosage of the mixtures, water/cementitious‐material ratio constant of 0.35 was used. The LWA were characterized by XRD, XRF, and SEM techniques. Compressive strength, water absorption, and volume change in magnesium sulfate solution (according to ASTM C1012 for a period of 15 weeks) of lightweight concretes were evaluated. It was found that the nanosilica had effect on refinement in the pore system; however, the main incidence on the compressive strength and durability of lightweight concrete (LWC) was defined by the characteristics of lightweight aggregate used in its preparation.

Effect of SiO2 and Al2O3 on characteristics of lightweight aggregate made from sewage sludge and river sediment

To attempt to solve the disposal problems of sewage sludge (SS) and river sediment (RS), these two types of sludge waste were used as the main raw materials for lightweight aggregate (LWA). SiO2 and Al2O3 are the main inorganic oxides of SS and RS. Little is known about their effects on LWA performance, although they are known to contribute to the formation of the basic skeleton structure. The main objective of this research was to systematically evaluate the effects of variations in SiO2 and Al2O3 content on characteristics of LWA, including physical characteristics, morphological structures, crystal phases, and stabilization of heavy metals. Our studies showed that LWA with the highest compressive strength, lowest porosity, and best solidification of heavy metals can be obtained with a SiO2 content between 30% and 45% and an Al2O3 content between 11% and 19%. Heavy metals were encapsulated within the aluminosilicate matrix structure when LWA pellets were sintered at 1100°C, indicating that harmful heavy metals can be solidified safely within LWA to increase the security, stability, and reliability of its application. Experimental results illustrated that SiO2 and Al2O3 are potentially crucial parameters that can control the physicochemical properties of LWA.

Strength degeneracy of LWAC and flexural behavior of LWAC members after fire

The characteristics of lightweight aggregate (LWA) with a low specific gravity and high water absorption will significantly change the properties of lightweight aggregate concrete (LWAC). This study aimed at exploring the effect of presoaking degree of LWA on the strength degeneracy of LWAC and flexural behavior of LWAC members exposed to elevated temperatures. The residual mechanical properties of the LWAC subjected to elevated temperatures were first conducted. Then, the residual load tests of LWAC members (beams and slabs) after exposure to elevated temperatures were carried out. The test results showed that with increasing temperature, the decreasing trend of elastic modulus for LWAC was considerably more serious than the compressive strength. Besides, the presoaking degree of LWA had a significant influence on the residual compressive strength and elastic modulus for LWAC after exposure to 800C. Moreover, owing to different types of heating, the residual load bearing capacity of the slab specimens were significantly different from those of the beam specimens.

Effect of the ratio of components on the characteristics of lightweight aggregate made from sewage sludge and river sediment

Previous studies shown that sewage sludge and river sediment can be used to produce lightweight aggregate (LWA). Control of the ratio of components in the LWA production process is important. In this study, we investigated the effect of mass ratio (K) of basic (Fe2O3, CaO, and MgO) and acidic (SiO2 and Al2O3) oxides on the characteristics of LWA. The studies show that LWA with lowest water absorption, the lowest solubility in hydrochloric acid and the highest grain density, the highest bulk density can be obtained when K in the range of 0.15–0.3, the properties of LWA in accordance with the standard of GB/T 17431.2-1998, China. When K was fixed at 0.2, the mass ratio of SiO2:Al2O3 in the range of 4:1–1:1 and the mass ratio of Fe2O3:CaO:MgO in the range of 5:2.2:1–1.7:1.9:1 resulted in LWA with the desired physical properties, the maximum compressive strength can reach 17.07MPa. The heavy metals experiments show that the leaching content (Cd, Cr, Cu and Pb) is closely related to a variation in K ratio, heavy metals can existed as stable crystalline compounds in LWA, and exhibiting excellent heavy metals solidification ability even it subjected to destruction, which indicates that stronger chemical bonds are formed between these heavy metals and the components through heat-induced transformation to the crystalline state. Investigations indicate that K can be a useful parameter to optimize LWA qualities.

Development of a method to test the pressurized absorption characteristics of lightweight aggregate

The pores of lightweight aggregates (LWAs) cause problems with the quality control and pumpability of lightweight aggregate concrete (LWAC), but offer a number of advantages in terms of weight saving and insulation. This paper presents pre-research for evaluating and predicting the pumpability of LWAC, which includes a test method developed for determining the pressurized absorption characteristics of LWAs. The test equipment needed for this consists of a pressure vessel combined with a plug to approximate a pump piston and provide pressurization by means of a loading device. A displacement meter is also included to measure the range of plug movement during pressurization. The testing procedure consists of six steps: adjustment of water levels, aggregate input, greasing, alignment, deaeration within the vessel, and finally pressurization with measurement. Equations to estimate porosity and provide a reference load-displacement curve are derived from the results of testing hollow spheres, and then applied to determining the absorbed void volume ratio of aggregate under pressure from the displacement of the plug. The pressurized absorptive characteristics of LWAs are also estimated by comparing the slope of their load-displacement curve to the reference curve. This reveals that the displacement of LWAC is highly dependent on the displacement of the LWA it contains.

Influence of volume fraction and characteristics of lightweight aggregates on the mechanical properties of concrete

The influence of lightweight expanded clay and shale aggregates on the mechanical performances of concrete is studied through their volume fractions and aggregate qualities. A very thorough characterisation of a series of LWAs is completed. The impact of aggregates is not only related to its particle density but also to the shell thickness, the percentage of large pores and broken grains. A reverse determination of the elastic modulus of LWA is carried out based to the experimental data. The comparison with values measured ultrasonically confirms the part played by the aggregate stiffer shell in mechanical properties of LWA.

Characteristics of lightweight aggregates from primary and recycled raw materials

In the following, a brief survey of mineral lightweight granules manufactured on the basis of a wide variety of constituents is given. After that, research projects conducted at the Tomsk Polytechnic University (Russian Federation) and Bauhaus University Weimar (Germany) are introduced that focus on the development of lightweight aggregates from new raw materials sources. In Tomsk, zeolitic rocks were used, while the investigations in Weimar concentrated on the sand fraction of masonry rubble mixed with autoclaved aerated concrete.