Properties Of Autoclaved Aerated Concrete Research Articles

Influence of a mortar type on shrinkage of autoclaved aerated concrete

AbstractShrinkage is one of the most important properties of Autoclaved Aerated Concrete (AAC), which is tested in accordance with EN 680:2008. Unfortunately, in construction, we have only a situation where AAC blocks are connected together with different types of mortar: standard mortar, thin joint mortar, or polyurethane glue. The shrinkage of masonry structures is determined by properties of AAC and properties of the used glue system. This research program, based on the standard EN 680, included AAC specimens of different density classes connected with various types of mortar: thin joint mortar with different compressive strengths, manufactured by various producers, and polyurethane glue. Specimens were prepared in accordance with the standard EN 680:2008, but connected by mortars in two different directions. Test results can be helpful in designing masonry structures.

Utilization of carbide slag in autoclaved aerated concrete (CS-AAC) and optimization: Foaming, hydration process, and physic-mechanical properties

Autoclaved aerated concrete (AAC), a lightweight porous material, has been widely used in the building field because of its energy savings. A solid waste called carbide slag with a high Ca(OH)2 content is a potential substitution for CaO to prepare AAC. In this study, carbide slag was used to replace quicklime to prepare carbide slag-based autoclaved aerated concrete (CS-AAC). The temperature, foaming rate, and rheological properties of the slurry during the foaming stage, the strength of the rough body, and the physical and mechanical properties of the autoclaved products were investigated. Hydration products, microstructure, and pore structure were further analyzed to investigate the mechanisms of carbide slag on the properties of AAC, and the use of sodium carbonate (SC) to improve the performance of CS-AAC was explored. The results show that the addition of carbide slag causes a degradation of the properties, including foaming rate and physic-mechanical properties. The “water locking” effect due to the irregular surface of the carbide slag results in an increase in slurry consistency. The increase in slurry consistency, as well as the decrease in slurry temperature is the main reason for the decrease in slurry foaming rate and roundness of bubbles, which are unfavorable for the strength development of AAC. Due to the alkali excitation characteristics of sodium carbonate. The addition of SC can react with Ca(OH)2 in the slurry to produce OH-, to promote cement hydration, which can accelerate the development of rough body strength, and save pre-curing time. The carbide slag-based AAC with 0.25% SC has a significant improvement in foaming properties and facilitates the generation of more C-S-H gels to form tobermorite under hydrothermal conditions, which improves the AAC properties. However, too much SC can consume a large amount of Ca(OH)2 and affects the production of tobermorite, which is not beneficial to the mechanical properties.

The effect of natural bamboo fiber and basalt fiber on the properties of autoclaved aerated concrete

Autoclaved aerated concrete (AAC) has the advantages of low density and good thermal insulation performance, but its mechanical properties are not so good. In this experiment, natural bamboo fiber and basalt fiber were used to strengthen AAC, and the effect of fiber content and fiber length on the AAC properties was investigated. The experimental results showed that with the increase of fiber content, the slurry fluidity, foaming height of AAC mixture decreased, the area of hazardous pore, the density, mechanical strength and thermal conductivity of AAC increased. As the fiber length increased, similar results were observed in the mechanical strength and thermal conductivity of AAC but not found in the slurry fluidity, foaming curve and pore structure. By contrast, natural bamboo fiber had greater impact on the properties of AAC than basalt fiber. The scanning electron microscope (SEM) results showed natural bamboo did not react with AAC matrix and the fiber was pulled out from AAC matrix when the AAC cracked, while basalt fiber was corroded in alkaline matrix and broke with AAC matrix together under external load.

Design, fabrication, and characterization of distinguished lightweight and sustainable building materials

As one of the eco-friendly building materials, autoclaved aerated concrete (AAC) has received considerable attention in industrial and academic research groups over the last few years. Herein, new AAC composites with different ratios of fine sand, lime, cement, and gypsum plaster were prepared in an autoclave at a pressure of 10 bar for 8 h. The effects of adding a polymelamine sulfonate (PMS) superplasticizer to the prepared AAC composites on workability were investigated according to their physical and mechanical properties. The binding phase of calcium silicate hydrate was fully characterized via Fourier transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The effect of AAC slurry foaming agent and water to solid ratio (W/S) was reported in detail. Furthermore, we studied the effect of ultrafine sand (<63 μm) reinforcement on the properties of AAC products.Under the specified curing conditions, the results showed that a strength value of 3.8 MPa with a low bulk density of 0.60 g/cm3 (600 kg/m3) was obtained from an AAC composite with 65 wt% fine sand, 15 wt% lime, 15 wt% cement, and 5 wt% gypsum plasters, containing 0.12 wt% Al powder and 45% water to solid ratio (W/S) mixtures. The strength value of the AAC composite can increase to 4.8 MPa, maintaining a low bulk density of 0.60 g/cm3 when the AAC slurry composite included 1% PMS at a W/S of 56% and 0.08% Al powder. In particular, the production of ultra low-density building materials can be efficiently controlled by mixing superplasticized AAC slurries with 0.16 wt% Al powder (at W/S = 56%), reaching a low bulk density of 0.39 g/cm3 (390 kg/m3) with a reasonable strength of 1.70 MPa for AAC samples. Interestingly, 50 wt% of fine sand with a particle size of about 90 μm is sufficient for tobermorite formation from the sand-lime reaction at designated hydrothermal conditions. However, replacing the large particles with ultrafine sand (<63μ) reduced the AAC strength characteristics. Besides, the compressive strength was improved by forming long tobermorite needles, lath structures, or both. In contrast, the gel-like material (poorly crystallized tobermorite) provides the lowest strength properties for AAC (about 3 MPa).

Influence of gypsum and limestone, used as mineral additives, on autoclaved aerated concrete properties

AbstractGypsum is a very popular mineral additive used in autoclaved aerated concrete (AAC) technology. In many studies, tobermorite can be synthesized from calcium‐silicate‐hydrate (C‐S‐H) phase under hydrothermal conditions in the presence of gypsum, and its impact on the tobermorite content in the AAC blocks has been discussed. It has been found in a previous study that tobermorite can be synthesized from katoite (Ca3Al2[SiO4]3‐x(OH)4x, where x = 1.5–3.0). Probably, it is the reason why Al additives accelerated tobermorite formation in the AAC process. Another very popular mineral additive is limestone. Calcite, in particular limestone, accelerates the reaction between alite with water and forms C‐S‐H phase, which may have an impact on tobermorite formation under hydrothermal treatment. The impact of limestone and gypsum as additives on phase composition and properties of AAC was determined. In the initial study on the laboratory scale, influence of limestone on the microstructure of AAC was determined. Later, on a technical scale, properties such as compressive strength, dry density, thermal conductivity coefficient, drying shrinkage, and phase composition for blocks of AAC containing gypsum additive or calcite additive were studied.

Effect of Aluminum Insertion Material on the Properties of AAC

Study on the compressive strength, shrinkage and effect of aluminum insertion materials on the hydration products of Autoclaved Aerated Concrete (AAC). The types and properties of hydration products are studied by X-Ray Diffraction Analysis (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscope analysis (SEM) and so on. The results showed that the strength and the shrinkage resistance capability of the product could be improved effectively. Al3+successfully doped into C-S-H gel and tobermorite crystals, then replaced si4+of tobermorite and formed the system of C-A-S-H. Tobermorite in aluminum insertion aerated concrete is smaller and more compact. All hydration products interlace to form a whole, then the structure turns denser. Low porosity, high crystal gel volume ratio and high hydration degree are the key of the high strength aluminum insertion aerated concrete. Aluminum insertion materials improve the performance of the products.

Effect of perlite waste addition on the properties of autoclaved aerated concrete

In presented paper, the influence of expanded perlite waste on the properties of autoclaved aerated concrete (AAC) was investigated. Expanded perlite waste was used as a quartz sand replacement in conventional AAC mixtures at 5%, 10%, 20%, 30% and 40% by weight. Results show that use of expanded perlite waste in AAC caused a unit weight decrease in the produced AAC, it is connected with the changes in the properties of AAC. The thermal conductivity coefficient and compressive strength of specimens decreased as the amount of expanded perlite waste increased in AAC. The introduction of perlite waste up to 10% by weight reduced the thermal conductivity about 15% without significant reduction of compressive strength. Further improvement of thermal conductivity may be obtained by the addition of perlite waste up to 30%, but it caused reduction compressive strength about 20%. The minimum thermal conductivity value was 0.074W/m·K, observed at 40% expanded perlite waste replacement. The structural and microstructural investigations showed that expanded perlite waste has a positive influence on the formation of calcium silicate hydrates (1.1nm tobermorite) in AAC. From this result, it was concluded that expanded perlite waste can potentially be used as quartz sand replacement in the production of AAC.

HUMIDITY INTRUSION EFFECTS ON THE PROPERTIES OF SOUND ACOUSTIC OF AUTOCLAVED AERATED CONCRETE

Autoclaved Aerated Concrete (AAC) has been commonly known to exhibit favorable thermal properties, hig h fire resistance and high compressive resistance at relatively low density. H owever, little attention has been devoted to the so und insulation performance of AAC. One of the points needs to know is humidity in trusion effects on AAC members in areas with high rhumidity levels of Mediterranean climates which are important in durab ility and insulation properties of AAC. Tests on me chanical and physical properties of ACC carried out to study humidity int rusion effects on AAC members were studied with and w/o coatings on the surfaces. From the findings of this study, physical and mechanical autoclaved aerated concrete evaluat ed in three different humidity levels to compare the effect of humidity on propert ies of AAC. According to test results coating is th e most important factor for improving resistivity of AAC walls, and these facto rs help AAC walls to keep their mechanical and phys ical properties against humidity. With its closed air pockets, AAC can prov ide very good sound insulation. This paper presents the results of studies on acoustic properties of AAC partitions aimed at iden tifying the effect of specific factors on AAC sound insulation performance.

Improving Mechanical Properties of Autoclaved Aerated Concrete by Sugar Sediment

The comparison of microstructure and mechanical properties between the autoclaved aerated concrete (AAC) and the autoclaved aerated concrete consist of sugar sediment (AAC-SS) was investigated in this work. The microstructure of AAC and AAC-SS was analyzed by the scanning electron microscopy (SEM). The mechanical properties of AAC and AAC-SS were focused on the compressive strength, the density, the water absorption and the flexural strength. To comfirm the tobermorite phase, the phase formation of the samples was tested using X-ray diffraction (XRD). It was found that the microstructure of AAC and AAC-SS surface was the finer needle-like crystalline morphology. The compressive strength (5.9 N/mm2) and flexural strength (1.82 N/mm2) of AAC-SS were higher than that of the AAC (5.0 N/mm2 and 1.64 N/mm2). While, the value of density (0.60 g/cm3) and humidity (23.59%) of AAC-SS had little less than that of the AAC (0.61 g/cm3 and 24.11%). The increasing of the tobermorite phase, which was added by the sugar sediment, had affected to the improvement of the mechanical properties. The specimens of both AAC and AAC-SS were claimed in quality class of 4, which based on the Thai Industrial Standard 1505-1998.