Mechanical Properties of Rammed Earth Stabilized with Local Waste and Recycled Materials

Traditional techniques of construction using natural and locally available materials are nowadays raising the interest of architects and engineers. Clayey soil is widely present in all continents and regions, and where available it is obtained directly from the excavation of foundations, avoiding transportation costs and emissions due to the production of the binder. Moreover, raw earth is recyclable and reusable after the demolition, thanks to the absence of the firing process. The rammed earth technique is based on earth compressed into vertical formworks layer by layer to create a wall. This material owes its strength to the compaction effort and due to its manufacture procedure exhibits layers resembling the geological strata and possessing high architectural value. The hygroscopic properties of rammed earth allow natural control of the indoor humidity, keeping it in the optimal range for human health. Stabilization with lime or cement is the most common procedure to enhance the mechanical and weather resistance at once. This practice compromises the recyclability of the earth and reduces the hygroscopic properties of the material. The use of different natural stabilizers, fibers, and natural polymers by-products of the agriculture and food industry, can offer an alternative that fits the circular economy requirements. The present study analyses the mechanical strength of an Italian earth stabilized with different local waste and recycled materials that do not impair the final recyclability of the rammed earth.

Energy evaluation of clay firing process and combustion gases in an intermittent kiln

The recording of temperatures in different positions in the firing process in an intermittent kiln to produce ceramic materials is presented, which led to the energy evaluation, determining the heat used for the clay firing process and the heat losses. In addition, a study of the emissions of pollutant gases released into the environment was carried out, as stipulated in the protocol of control, and monitoring of stationary source. In the energy balance, large energy losses were detected in heat accumulation in the masonry of 7.20×106 KJ of the energy supplied, representing 16.99%, and in the kiln walls of 5.20×10 KJ, representing 12.17%. As a result, it is necessary to make constructive and operative changes in the operation of the kilns, which will lead to the recovery of residual heat in the use of drying of parts, drying, and preheating of combustion air, reducing energy consumption and emissions of pollutants into the atmosphere. The average concentration of particulate matter released into the environment was 1056.60 mg/m3, 422% higher than the standard, affecting people’s health.

Recycling Cigarette Butts in Ceramic Tiles

Cigarettes are one of the favoured commodities on our planet. However, the annual consumption of 5.7 trillion cigarettes and 75% littering rate results in cigarette butts (CBs) being one of the most critical environmental issues. The leachate of heavy metals and toxic chemicals is polluting our ecosystem and threatening the wildlife species. Therefore, it is crucial to find effective and efficient recycling methods to solve the growing CB waste issue. In this study, unglazed fired ceramic tiles were manufactured with 0%, 0.5%, 1.0%, and 1.5% shredded CBs by dry mass to investigate the feasibility of the proposed sustainable recycling method. The chemical and mineralogical characterisation, density, shrinkage, bulk density, breaking strength, water absorption, and modulus of rupture were investigated and compared with the Australian Standards for ceramic tiles (AS 4459). The results revealed that tiles incorporating 0.5% CBs by mass demonstrated the greatest performance compared to the other mixtures. The water absorption for all tile–CB mixtures was found to be greater than 10%, with a positive growth tendency. The addition of 0.5% CBs by mass slightly improved flexural strength from 15.56 MPa for control samples to 16.63 MPa. Tiles containing 0.5% CBs by mass satisfied the modulus of rupture and water absorption limits for group III class according to the Australian Standards (AS 13006), and they may be suitable to be used as wall tiles. The result of a simulation equation predicts that an energy savings of up to 7.79% is achievable during the firing process for ceramic tiles incorporating 1% CBs by mass.

Volcanic Tuff as Secondary Raw Material in the Production of Clay Bricks

The present work examines an innovative manufacturing technique for fired clay bricks, using tuff as a secondary raw material. Samples were made of clay and tuff (0–30 wt.%) fired at 900 to 1100 °C. The chemical and mineralogical compositions and physical and thermal analyses of raw materials were investigated by using SEM-EDS, RX and DTA-TG curves. The samples were analysed from the mineralogical, technological and mechanical points of view. The result show that the tuff’s presence in the clay mixtures considerably reduced the shrinkage of the product during the firing process, and the manufactured samples were of excellent quality. The compressive strength of the bricks varied from 5–35.3MPa, being influenced by the tuff content, clay matrix properties and firing temperatures. Finally, the heat demand for increasing the temperature from room to the firing temperature of the sample with 10% tuff content was 22%.

Reacting Flow Characteristics and Multifuel Capabilities of a Multi-Nozzle Dry Low NOx Combustor: A Numerical Analysis

The fluctuating quality of natural gas (NG) in Peninsular Malaysia (PM) makes it challenging for the gas turbine (GT) combustor to meet the combustion performance requirements from the Original Equipment Manufacturer (OEM). Moreover, the gas quality sensitivity is more apparent in modern dry low NOx (DLN) combustors. Many of the prior combustion investigations were conducted on a modest scale in the laboratory. In actuality, combustion characterizations in complicated DLN combustors are more valuable to the power generation sector. Hence, the current numerical analysis utilized the RANS formulation and a detailed chemistry to examine the impact of ethane (C2H6), carbon dioxide (CO2), and nitrogen (N2) proportions in NG on combustion characteristics in a multi-nozzle DLN (MN-DLN) combustor, with the support of Modified Wobbe Index (MWI) calculations. Validations were performed using the combustor outlet temperature (COT) from the power plant where the actual MN-DLN combustor is operated, which revealed less than 10 % discrepancy. Qualitative validations were carried out by comparing the burn trace from the actual combustor wall to the predicted results, revealing an adequate Structural Similarity Index (SSIM) of 0.43. From numerical results of flame fronts and COTs, the addition of 20 % diluents (CO2 and N2) to NG demonstrated the blowoff risk. When MWIs of Kerteh and the JDA (major NG resources) were used as baselines, MWI ranges of all NG compositions under study surpassed the OEM’s ± 5 % limit. The increase in CO2 proportion results in a wide MWI range, especially when Kerteh is used as the baseline. Therefore, any GTs in PM that have previously been calibrated to use Kerteh's NG are more likely to have combustion instabilities if CO2 levels in NG suddenly increase. The higher MWI range backs up the current numerical results that showed the deleterious effects of a high CO2 composition throughout the combustor firing process. However, increasing the amount of C2H6 by up to 20 % is predicted to have minor effects on combustion characteristics. Overall, the validated numerical model of the MN-DLN combustor provided critical information about combustion characteristics and multifuel capabilities in respect to the NG quality in PM.

Energy lost in endothermic reactions in the production of clay blocks in a continuous kiln

In Ocaña, Norte de Santander, Colombia, the production of ceramic materials is done in a traditional and empirical manner, generating heat losses, low productivity and product quality, and increased emissions of polluting gases into the environment. A virtual instrument for temperature data acquisition was developed and the firing process was monitored in two loading doors of a Hoffman kiln. 29040 blocks were produced, and 1370.76 kg of pulverized charcoal were consumed. The firing process lasted sixty-two hours and the virtual instrument was programmed to record data every 5 minutes. The energy supplied to the brick kiln was 340.16x106 kJ and the heat due to loading of the products and heat lost in the endothermic reactions of the clay was 107.71x106 kJ and 105.71x106 kJ respectively, representing 31.66% and 31.08% of the energy supplied. The results have made it possible to establish trends in the temperatures and energy consumed in the endothermic reactions in the clay. This will allow the implementation of coal quality and grinding procedures, increasing energy efficiency, and reducing gas emissions into the environment, thus avoiding acute respiratory diseases.

Decomposition of Crystalline Limestones during the Burning Process

The decomposition of limestone during the firing process is mainly based on the decarbonation of CaCO3. In the case of crystalline limestone, it is the decomposition of calcite crystals. In this study, different limestone properties on the course of decarbonation are studied. Therefore, the samples are determined from a geological and physicochemical point of view (geological age and origin, total porosity, limestone category, chemical analyses and insoluble residue). After thorough identification of the samples, various analyses focused on limestone and lime microstructure are performed, such as SEM image analysis or lime reactivity. For these analyses, the samples are burned at different temperatures. The decrepitation amount of limestones during burning process is determined.

Recording of temperatures and heat accumulation in masonry in a continuous kiln used to produce ceramic materials

In Ocaña, Colombia, a traditional ceramic industry has been developed using low efficiency kilns without controls in the combustion processes, which generate large heat losses. As a result, it was necessary to implement a virtual instrument to monitor temperatures in the firing process. For the study, a continuous Hoffman kiln, and the temperature acquisition was carried out in two combustion chambers and lasted twenty-four hours. In the kiln firing process, the energy supplied due to coal combustion was 22198×106 KJ, while the heat accumulated in the kiln roof, walls and floor was 14452.6×106 KJ, 1085.71×106 KJ and 164.72×106 KJ respectively. The total heat stored in the masonry was 15703.03×106 KJ, representing 70.73 % of the energy supplied. Due to the material used in the construction of the kiln, the accumulated heat is high, and it is necessary to implement coatings using ceramic fibers on the kiln walls, keeping the temperature constant in the firing process and leading to a decrease in heat accumulation of about 20 %. Also, air, fuel, temperature, and pressure injection systems should be implemented.