Manufacture Of Lightweight Aggregate Research Articles

Bloating zone of artificial lightweight aggregates in triaxial whiteware compositions using ME-DOE

This study examines the characteristics of manufactured aggregates by designing an experiment using Mixture Experiments Design of Experiments (ME-DOE) for triaxial whiteware compositions and proposes the optimal mixture for manufacturing artificial lightweight aggregates. The optimal mixture designed using ME-DOE was manufactured in a pilot-scale rotary kiln. The density and water absorption rate of the manufactured aggregates were measured, and the cross-section was observed. Additionally, Mercury Intrusion Porosimetry (MIP) and 3D-CT observation were conducted to observe the pores. The samples designed using the ME-DOE were classified into five types based on the internal microstructure, which had a high correlation with the physical properties of the aggregates. The matrix composition, excluding Fe2O3 and carbon in the area where the black core was created and bloated, was formed in the area of a typical triaxial whiteware mixture. Lightweight aggregates were manufactured at the Pilot Rotary Kiln using a 50:50 mixture of feldspar and ball clay, and the manufactured lightweight aggregates met ASTM C330 standards.

Experimental study on properties of cinder aggregate lightweight concrete with fibre reinforcement

Lightweight concrete is gaining increasing significance in the construction industry due to its numerous advantages over conventional concrete. It can be produced by partially or fully replacing conventional coarse aggregates with lightweight aggregates. Laboratory tests were conducted to assess the feasibility of utilizing solid waste, such as cinders, for manufacturing lightweight aggregate concrete. The mechanical properties of cinder aggregate lightweight concrete were improved through the introduction micro-reinforcements. Polypropylene fibres were incorporated as micro-reinforcements at volume fractions of 0.1%, 0.2%, 0.3%, and 0.4%. The experimental results, including compressive strength, flexural strength, and modulus of elasticity, demonstrated that waste cinder aggregates can effectively replace coarse aggregates in lightweight concrete. Furthermore, the incorporation of polypropylene fibres enhances the mechanical performance of cinder aggregate lightweight concrete.

A study of characteristics of man-made lightweight aggregate and lightweight concrete made from expanded polystyrene (eps) and cement mortar

Abstract This research investigated the feasibility of using waste-expanded polystyrene (EPS) and mortar to produce lightweight aggregate (LWA). The EPS extracted from the leftover backing waste was crushed into beads using an electric grinder and mixed in three different proportions with two types of mortars (with and without a superplasticizer). Physical property tests such as loose bulk density and water absorption were carried out for the LWA. Also, the compressive strength of the manufactured lightweight aggregate concrete (LWAC) was determined, and failure modes were discussed. The results indicate that using the EPS is effective for LWA. The loose bulk density is obtained at a range from 588 to 790 kg/m 3 790\hspace{0.33em}{\text{kg/m}}^{3} , which meets the requirements of the American society for testing and materials C330 specification of LWA. For water absorption, the value obtained ranges from 6.45 to 14.05%, slightly higher than the normal aggregate due to the voids in the LWA. When using LWA containing a superplasticizer to produce LWAC, the compressive strength was higher than the concrete with LWA without a superplasticizer. The highest compressive strength for LWAC was 21 MPa.

Lightweight SCC Development in a Low-Carbon Cementitious System for Structural Applications.

The utilization of manufactured lightweight aggregates adds another dimension to the cost of the preparation of self-compacting concrete (SCC). The common practice of adding absorption water to the lightweight aggregates before concreting leads to inaccurate calculations of the water-to-cement ratio. Moreover, the absorption of water weakens this interfacial bond between aggregates and the cementitious matrix. A particular type of black volcanic rock with a vesicular texture known as scoria rocks (SR) is utilized. With an adapted sequence of additions, the occurrence of water absorption can be minimized to overcome the issue of calculating the true water content. In this study, the approach of preparing the cementitious paste first with adjusted rheology followed by the addition of fine and coarse SR aggregates enabled us to circumvent the need for adding absorption water to the aggregates. This step has improved the overall strength due to the enhanced bond between the aggregate and the cementitious matrix, rendering a lightweight SCC mix with a target compressive strength of 40 MPa at 28 days, which makes it appropriate for structural applications. Different mixes were prepared and optimized for the best cementitious system that achieved the goal of this study. The optimized quaternary cementitious system included silica fume, class F fly ash, and limestone dust as essential ingredients for low-carbon footprint concrete. The rheological properties and parameters of the optimized mix were tested, evaluated, and compared to a control mix prepared using normal-weight aggregates. The results showed that the optimized quaternary mix satisfied both fresh and hardened properties. Slump flow, T50, J-ring flow, and average V-funnel flow time were in the ranges of 790-800 mm, 3.78-5.67 s, 750-780 mm, and 9.17 s, respectively. Moreover, the equilibrium density was in the range of 1770-1800 kg/m3. After 28 days an average compressive strength of 42.7 MPa, a corresponding flexural load of over 2000 N, and a modulus of rupture of 6.2 MPa were obtained. The conclusion is then drawn that altering the sequence of mixing ingredients becomes a mandatory process with scoria aggregates to obtain high-quality lightweight concrete for structural applications. This process leads to a significant improvement in the precise control of the fresh and hardened properties, which was unachievable with the normal practice used with lightweight concrete.

The Corrosion Resistance of Reinforced Lightweight Aggregate Concrete in Strong Brine Environments.

Taiwan has used technology in reservoir sediments and industrial waste to produce high-performance lightweight aggregate (LWA). LWA can be used to manufacture lightweight aggregate concrete (LWAC) with structural strength ratings. At present, Taiwan's offshore wind turbines are gradually developing and are moving from coastal areas to deep-sea areas. With this in mind, this study aimed to investigate the feasibility of applying LWAC with synthetic LWA from reservoir sediments to floating offshore wind turbine foundations. LWAC and normal-weight concretes (NWC) of different strengths were prepared, and their fresh, hardened, and durability properties were tested. In addition, reinforced concrete and steel sheets were immersed in a tank of high salinity seawater to examine their resistance to seawater-accelerated corrosion. The test results showed that the total passing charge of the two groups of concrete within six hours was less than 1000 coulombs. Both groups of concrete were classified as having "Very Low" chloride permeability. The average corrosion potential of most reinforced concrete specimens was found to be greater than -200 mV, which means that the corrosion probability of the steel bars was less than 10%. Furthermore, the use of coatings for seawater corrosion protection on steel sheets was not found to be as effective as reinforced concrete. This shows that the use of LWAC with synthetic LWA from reservoir sediments for the floating foundations of offshore wind turbines is feasible and has design flexibility.

Eco-efficient transformation of mineral wool wastes into lightweight aggregates at low firing temperature and associated environmental assessment

Waste recycling is one of the key elements to mitigate the environmental problems that threaten our society. Mineral wool is currently the most widely used insulation material in the European Union, so the amount of waste generated in the demolition and restoration of buildings has increased alarmingly. This work investigates for the first time the use of glass wool (GW) and rock wool (RW) as a component in the manufacture of lightweight aggregates, showing that both can be suitable raw materials considering the density (1.3–1.5 g/cm3) and mechanical strength (2–6 MPa) obtained. In addition, the use of GW would help to reduce the firing temperature significantly (700 °C) compared to that normally used in the manufacture of these materials (around 1200 °C), which would imply significant energy savings. Considering that thermal insulation materials and lightweight aggregates are among the most widely used materials in the construction sector, the work presented here also evaluates the environmental impact associated with the manufacture of lightweight aggregates with RW and GW in comparison with the traditional process, using the Life Cycle Assessment (LCA) methodology. A significant environmental improvement has been observed in almost all the analyzed impact categories of the artificial aggregates manufactured with mineral wool with respect to traditional LWAs.

Performance of manufactured aggregate in the production of sustainable lightweight concrete

This study examines the performance of lightweight concrete incorporating manufactured lightweight aggregates with industrial by-products. The physical and mechanical properties of cold-bonded aggregates manufactured through pelletization technique with 80% fly ash, 10% cement, and 10% metakaolin with the addition of 0.2% alkali-resistant glass fibers. The manufactured aggregates have been tested with different properties like production efficiency, bulk density, specific gravity, water absorption, and impact strength thereby compared with natural aggregate results. Further, the study on properties of lightweight concrete produced with the replacement of ordinary portland cement (OPC) by ground granulated blast furnace slag (GGBFS) at different percentages varies from 0% to 50%. The lightweight concrete performance was assessed based on the slump cone test, density, compressive strength, split tensile strength, and water absorption at different curing ages. It was noticed from the results that the optimum performance of lightweight concrete was attained at 40% replacement with GGBFS. It is observed from the results that the replacement of natural aggregate by manufactured aggregates and cement by GGBFS achieved desired strength to be used as a structural material. Usage of industrial by-products in aggregates and concrete production results in both economic and environmental benefits.

Use of ballasted flocculation (BF) sludge for the manufacturing of lightweight aggregates

Ballasted flocculation (BF) is an efficient way to remove the turbidity from surface water. The objective of the present study is to optimize the ballast (magnetite), coagulant (poly aluminum chloride) concentration and pH for efficient turbidity removal from surface water. To do this, the sludge produced from an optimized dose of a BF treatment was utilized for the production of lightweight (LW) aggregates by combining it with hard clay and sewage sludge. The LW aggregates were formed by means of rapid sintering in the temperature range of 1000–1200 °C with an exposure time of 10 min. The physical properties of the LW aggregates, in this case the leaching of heavy metals, the bulk density and the microstructure, were investigated. The results indicated that corresponding ballast and coagulant concentrations of 0.75 g/L and 30 mg/L (poly aluminum chloride (PAC)) resulted in the maximum removal efficiency of ≈95%. Using a mixture of BF sludge (30 wt%), dry sewage sludge (20 wt%), and hard clay (50 wt%), aggregates with a density of around 1.0 g/cm3 could be produced. In addition, it was confirmed that the manufactured aggregate was environmentally stable as the elution of heavy metals was suppressed.

Effect of sintering temperature on lightweight aggregates manufacturing from copper contaminated soil

Manufacturing lightweight aggregate (LWA) at high temperature is an effective way to immobilize heavy metals in solid waste. This work investigated the performance and solidification mechanism of LWA prepared from copper contaminated soil. The volume expansion of LWA could reach a maximum of 28%, and its lowest density accounted of 1.5 g/cm3, which met the standard requirements. Optical microscope and micro-CT test illustrated that the addition of Cu leaded to obvious phase separation in LWA. The Cu leaching result of LWA first increased and then dropped with the temperature. The XRD test found that the main formation phase of Cu in LWA were t-CuFe2O4 and amorphous phase that they had different acid resistance ability. XPS revealed that the main cause of the agglomeration of liquid phase in LWA was the chain broken reaction between Cu and Si–O tetrahedron. SEM-EDS results showed that the distribution of Cu and Si had a strong correlation, which meant that Cu mostly formed amorphous phase. This work showed the uniqueness of Cu in the high temperature immobilization and pointed out the best immobilization target phase.

Manufacturing and application of artificial lightweight aggregate from water treatment sludge

The purpose of this study is to manufacture lightweight aggregates for the recycling of water treatment sludge (WTS), to identify the physical properties of the aggregates, and to present a means by which to utilize the manufactured lightweight aggregates. The chemical composition and thermal properties were examined via a raw materials analysis. The aggregate examined here was fired by the rapid sintering method and the single-particle density and water absorption rate were measured. WTS has a high LOI and the calcined inorganic material has high refractoriness. When 30 wt% of purified sludge was added, the single-particle density of the aggregates was in the range of 0.8–1.2g/㎤ at temperatures of 1150–1200 °C. At temperatures of 1200 °C or higher, ultra-lightweight aggregates having a single-particle density of 0.8 or less could be produced. When applied to concrete by replacing the general aggregate in the concrete, a specimen with strength values of 20–45 ㎫ at 28 days was obtained, and when applied as a filter material, the performance was equal to or exceeded that of ordinary sand.

Sintering of sepiolite-rich by-products for the manufacture of lightweight aggregates: technological properties, thermal behavior and mineralogical changes

A sepiolite mining by-product (SEP) has been studied as major component for lightweight aggregate (LWA) manufacture. Pellet bursting during firing was avoided by the addition of 2.5 wt% of thermoplastic waste (P) and 2.5 wt% P + 2.5 wt% carbon fiber residue (FC) in powder form. The mixtures were pelletized and then sintered at 1225º˚C for 4 minutes in a rotary kiln. Highly porous white LWAs with good mechanical strength were produced. A mineralogical study revealed the formation of amorphous phase ( > 50%) and minor proportions of enstatite, protoenstatite and diopside. Quartz was the only inherited mineral, appearing in the form of isolated phenocrysts within a general porphyritic texture. The result of this study suggests the promising use of sepiolite (whether or not in residue form) for the manufacture of high quality LWAs.

Using scheelite residue and rice husk ash to manufacture lightweight aggregates

Over the years, the use of expandable clays has supported the world production of lightweight aggregates (LWAs), however the gradual lack of natural resources requires using more sustainable practices. Thus, the aim is to develop LWAs suitable for use in structural lightweight concrete and other engineering services, using scheelite residue (SPR) and rice husk ash (RHA). Studies show that the production of these residues is increasing, their environmental impacts are significant, and their properties favour the development of LWAs. However, no research was found on the use of SPR in LWAs. Raw materials were characterised by laser granulometry, scanning electron microscopy, X-ray fluorescence, X-ray diffraction and simultaneous thermal analysis. Then, 23 mixtures were formulated, from the replacement of clay by up to 100% residues. The samples were sintered at 1100, 1150, 1200 and 1250 °C. The manufactured aggregates were characterised by the bloating index (BI), mass loss (LOI), particle density (ρd), water absorption (WA24H), crushing strength (S), mineralogical composition and microstructure. Finally, the feasibility of using the manufactured LWAs was evaluated, based on a comparative analysis with the properties of a commercial LWA. The resulting aggregates showed: (BI) maximum of 77.44%, (LOI) of up to 12.0%, (ρd) varying between 0.86 and 1.80 g/cm3, (WA24H) minimum of 2.0% and (S) up to 13.5 MPa. Overall, 42 specimens demonstrated properties at least similar to the commercial LWA ones. The results reveal that it is technically feasible to use SPR and RHA to produce LWAs.

Manufacturing of Lightweight Aggregates as an Auspicious Method of Sewage Sludge Utilization.

Sewage sludge is a high-volume and low-cost waste commonly generated worldwide, so its utilization is a vital issue. The application of this waste in the manufacturing of lightweight aggregates was investigated. The process was performed using intensive mixers with volumes of 5 and 30 L, as well as the industrial 500 L mixer. Then, granulates were sintered in a tube furnace. The influence of composition and mixer size on the particle size, microstructure, mechanical performance, and stability of lightweight aggregates in different environments was analyzed. The best results were obtained for a 500 L mixer, enhancing the industrial potential of the presented process. Increasing the share of sewage sludge in the composition of aggregates enhanced their porosity and reduced the specific weight, which caused a drop in compressive strength. Nevertheless, for all analyzed materials, the mechanical performance was superior compared to many commercial products. Therefore, sewage sludge can be efficiently applied as a raw material for the manufacturing of lightweight aggregates. The presented results confirm that a proper adjustment of composition allows easy the tailoring of aggregates’ performance and cost.

Utilization and assessment of recycled polyethylene terephthalate strapping bands as lightweight aggregates in Eco-efficient composite mortars

In this work, we explored the possibility of using aggregates of shredded polyethylene terephthalate strapping bands (SPETSB) in mortar. A survey was carried out to assess the feasibility of recycling this plastic waste to be used in the manufacture of environmentally-friendly lightweight mortars through partial replacement of silica-calcareous sand with lighter SPETSB aggregates, by volume at 0, 15, 30, 45 and 60 %. A scanning electron microscopy analysis along with a study of the alkali – silica reaction was conducted; the density, mechanical and thermal properties were assessed for evaluating the properties of lightweight mortar containing SPETSB aggregates (LWMSB). Laboratory tests revealed encouraging results and confirmed the feasibility of manufacturing lightweight aggregate mortar with a density between 1620 and 1944 Kg/m3, a compressive strength equal to 28.8 MPa and thermal conductivity of 0.75 W/m.K, at 28 days, for 60% of SPETSB. The flexural strength, ultrasonic pulse velocity (UPV) and dynamic elastic modulus (Ed) were lower by 46%, 25% and 56%, respectively, compared to the values of normal weight mortar (NWM). This study also allowed deducing that the expansion due to the alkali–silica reaction decreases for all LWMSB types, when the substitution rate of SPETSB increases; this makes it possible to obtain a non-reactive mortar. Therefore, these findings suggest that using LWMSB composite mortars in building applications is possible.

Experimental & computational study on fly ash and kaolin based synthetic lightweight aggregate

The objective of this study is to manufacture environmentally-friendly synthetic lightweight aggregates that may be used in the structural lightweight concrete production. The cold-bonding pelletization process has been used in the agglomeration of the pozzolanic materials to achieve these synthetic lightweight aggregates. In this context, it was aimed to recycle the waste fly ash by employing it in the manufacturing process as the major cementitious component. According to the well-known facts reported in the literature, it is stated that the main disadvantage of the synthetic lightweight aggregate produced by applying the cold-bonding pelletization technique to the pozzolanic materials is that it has a lower strength in comparison with the natural aggregate. Therefore, in this study, the metakaolin made of high purity kaolin and calcined kaolin obtained from impure kaolin have been employed at particular contents in the synthetic lightweight aggregate manufacturing as a cementitious material to enhance the particle crushing strength. Additionally, to propose a curing condition for practical attempts, different curing conditions were designated and their influences on the characteristics of the synthetic lightweight aggregates were investigated. Three substantial features of the aggregates, specific gravity, water absorption capacity, and particle crushing strength, were measured at the end of 28-day adopted curing conditions. Observed that the incorporation of thermally treated kaolin significantly influenced the crushing strength and water absorption of the aggregates. The statistical evaluation indicated that the investigated properties of the synthetic lightweight aggregate were affected by the thermally treated kaolin content more than the kaoline type and curing regime. Utilizing the thermally treated kaolin in the synthetic aggregate manufacturing lead to a more than 40% increase in the crushing strength of the pellets in all curing regimes. Moreover, two numerical formulations having high estimation capacity have been developed to predict the crushing strength of such types of aggregates by using softcomputing techniques: gene expression programming and artificial neural networks. The R-squared values, indicating the estimation performance of the models, of approximately 0.97 and 0.98 were achieved for the numerical formulations generated by using gene expression programming and artificial neural networks techniques, respectively.

Evaluation of the Environmental Benefits Associated with the Addition of Olive Pomace in the Manufacture of Lightweight Aggregates.

A Life Cycle Assessment (LCA) using SimaPro software has been carried out concerning the manufacture of artificial lightweight aggregates (LWAs). The study aims to evaluate the changes in the environmental impact when an additive of residual origin, specifically olive pomace (OP), is added following the principles of the Circular Economy. This residue (commonly known as alperujo) was used as a substitute for clay in 1.25, 2.5 and 5 wt%. The environmental impact related to the use of olive pomace in the mixture was estimated using the CML 2000 methodology, yielding improvements of 3.8%, 7.7% and 15.3% for 1.25, 2.5 and 5 wt% OP added, respectively. Optimum addition results are in the range of 1.25 and 2.5 wt% OP. In this way, the reduction of emissions associated with LWA manufacture would be favored without negatively affecting the technological properties of the resulting material.

Composition design of the optimum bloating activation condition for artificial lightweight aggregate using coal ash

This study analyzed the characteristics of reject ash and bottom ash as raw materials for lightweight aggregate and suggested an optimum mixing ratio for recycling coal ash. The physical and chemical properties of reject ash and bottom ash for the manufacture of lightweight aggregate were examined. Rapid sintering tests were conducted to find an optimum mixing ratio to produce lightweight aggregates, density was measured, and cross-sections were observed. XRD-CT analysis was performed to observe the crystal phase distribution of the lightweight aggregate. Aggregate was sintered in a pilot rotary kiln using the optimum mixing ratio obtained through the experiment and its properties were measured. Coal ash has been found to be an unsuitable raw material for producing lightweight aggregate. By adding 3 wt% of carbon and 5 wt% of Fe2O3 to the bottom ash-dredged soil mixture, it was possible to prevent the adhesion of aggregate at the bloating activation temperature by lowering the firing temperature. Aggregates manufactured in the pilot rotary kiln meet the relevant standards and exhibit properties similar to those of commercial aggregates.

Recycling of ‘alperujo’ (olive pomace) as a key component in the sintering of lightweight aggregates

Abstract The current environmental problems that threaten our society can only be mitigated with a radical change in the paradigm of production and consumption. Recycling waste is a key element in this. This work has focused on the valorization of a widely spread agricultural waste: the so-called ‘alperujo’ (olive pomace). For the first time, olive pomace (OP) has been used as a component in the manufacture of lightweight aggregates (LWAs). Mixtures with 0, 1.25, 2.5, 5 and 10 wt% OP have been prepared from three different clays. The research results show that the addition of OP in low proportions (mainly 2.5%) is more positive to achieve aggregate bloating, pore formation and a lighter structure. The high calorific value of OP also helps to reduce the firing temperature significantly, which would result in energy savings. In the same way, bloating would be favored with the increase of the time and the temperature, especially with this last one. The materials obtained have excellent properties. In addition, the study of leachate in the most expanded aggregate shows that the concentration of heavy metals is very low, representing no danger to the environment. According to these findings, the recycling of olive pomace can be an excellent alternative in the manufacture of LWAs.

Manufacturing of lightweight aggregates from biomass fly ash, beer bagasse, Zn-rich industrial sludge and clay by slow firing

A 70:30 black-white clay mixture (C) has been blended with different proportions of three wastes: bagasse from beer production (BG), a flux sludge used in galvanization (FS) and fly ash enriched to 60% with K2O from a biomass plant (FA). A complete characterization of the raw materials was performed. Mixtures of C and FA for 15, 17.5 and 20 wt% of K2O were blended with water, shaped into prismatic specimens, oven-dried, muffle-sintered at 1000–1200 °C, and finally crushed into lightweight aggregates (LWAs). The amounts of FA corresponding to K2O = 20% for a temperature, T, of 1000 °C (LWA variety C20K-1000) yielded the best technological properties: oven-dry density of 1.22 g/cm3, water absorption of 39.8% and open porosity of 48.6%. Therefore, other specimens containing BG and FS were sintered according to the same protocol considering K2O = 20% and T = 1000 °C. White aggregates were also obtained at 1000 °C (C-1000 variety) from C-mixture (without FS, FA and BG). The addition of BG (5,7 and 10 wt%) did not mean any improvement with respect to C20K-1000, and in the case of FS (25–40%), the development of red color was fostered, which could be interesting for gardening or ornamental purposes. A leaching test conducted on the aggregate with 40 wt% FS showed that the concentration of heavy metals was below the permitted environmental thresholds. Although the leachable Zn concentration of the aggregate (205 ppm) was reduced by 85% with respect to the original residue, it is still high enough for crops that demand this metal. The outcome of this investigation proves the usefulness of recycling agricultural and industrial wastes to obtain high quality LWAs for agriculture or gardening.

Rapid sintering of weathered municipal solid waste incinerator bottom ash and rice husk for lightweight aggregate manufacturing and product properties

This study assessed the technical feasibility of formulating lightweight aggregates (LWA) from municipal solid waste incinerator bottom ash (IBA) and residual biomass. Weathered IBA (WIBA) particles larger than 8 mm contain a mixture of calcium-rich compounds and other silicates mainly composed of glass and synthetic and natural ceramics, with low contents of heavy metals and soluble salts. Unfired LWA were formulated with the particle size fraction of WIBA larger than 8 mm and rice husk (RH) used as the bloating agent. Rapid sintering of the unfired spherical pellets at 1,100 °C for 5 min produced some cohesive sintered LWA, whose porosity, apparent particle density, water absorption, and compressive strength directly correlated with the percentage of RH added. The fired LWA formulated with 5 wt% of RH showed the highest bloating index (115%) and porosity (53%) and the lowest apparent particle density (0.61 Mg m−3) and compressive strength (1.4 MPa). The addition of more than 5 wt% of RH increased the internal temperature of the sintered aggregates and decreased the viscosity of the molten glassy materials, resulting in the collapse of the inner structure. Consequently the porosity decreased and the apparent density of the particles increased, thereby shrinking the volume of the fired LWA. According to the standard leaching test (EN 12457–4), both the unfired precursor and the sintered aggregates showed concentrations of heavy metals and metalloids in the leachates that were well below the safety limits established for their reuse as secondary materials.