Synthesis and Microstructure Analysis of Autoclaved Aerated Concrete with Carbide Slag Addition

Synthesis of autoclaved aerated concrete （AAC） has been carried out with carbide slag addition, and the carbide slag could be used as a main material to produce the AAC with the compressive strength about 2 MPa and the density below 0.6 g.cm-3. In this study, quartz sand acted as frame structure phase in the matrix, and quartz addition also influenced the Si/Ca of starting material. Tobermorite and CSH gel were formed readily at 62%, which seemed to enhance the compressive strength of samples. Curing time seemed to affect the morphology of phase produced, and specimen with the plate-like tobermorite formed at 10 h appeared to have a better compressive strength development than the fiber-like one at 18 h. The higher curing temperature seemed to favor the tobermorite and CSH gel formation, which also exerted a significant effect on the strength development of the samples. On the micro-scale, the formed CSH gel was filled in the interface of the matrix, and the tobermorite appeared to grow in internal-surface of the pores and interstices. The tobermorite or/and CSH formation seemed to densify the matrix, and therefore enhanced the strength of the samples.

A Review on the Utilization of Waste Material for Autoclaved Aerated Concrete Production

Autoclaved aerated concrete(AAC)has become more attractive due to its excellent and environmental-friendly properties in building construction.AAC is relatively lightweight,possesses lower thermal conductivity,higher heat resistance,lower shrinkage,and fasten construction than normal concrete.AAC is a combination of silica sand,cement,gypsum,lime,water,and an expansion agent.To improve its physical and mechanical properties and reduce its production cost,tremendous innovations where waste materials were utilized as partial replacement of AAC materials were done.This paper is intended to present the literature on the utilization of waste materials as a means of a partial replacement in AAC materials to enhance its physical and mechanical properties and thermal performance.The physical properties such as microstructure and mechanical properties such as density,compressive strength,water absorption are presented to classify the investigation that has been done in such innovations.Apart from that,the discussion on innovations to improve its thermal performance was also presented.Based on the review,an increase of AAC application causes much waste at construction sites and recycling concrete waste powder into wall concrete;particularly,an AAC was not frequently practiced in construction.

Preparation of New Cementitious System using Fly Ash and Dehydrated Autoclaved Aerated Concrete

We experimentally studied the interaction between pozzolanic material（fly ash） and dehydrated autoclaved aerated concrete（DAAC）. The DAAC powder was obtained by grinding aerated concrete waste to particles fi ner than 75μm and was then heated to temperatures up to 900 ℃. New cementitious material was prepared by proportioning fly ash and DAAC, named as AF. X-ray diffraction（XRD） was employed to identify the crystalline phases of DAAC before and after rehydration. The hydration process of AF was analyzed by the heat of hydration and non-evaporable water content（Wn）. The experimental results show that the highest reactivity of DAAC can be obtained by calcining the powder at 700 ℃ and the dehydrated products are mainly β-C2 S and CaO. The cumulative heat of hydration and Wn was found to be strongly dependent on the replacement level of fl y ash, increasing the replacement level of fl y ash lowered them in AF. The strength contribution rates on pozzolanic effect of fl y ash in AF are always negative, showing a contrary tendency of that of cement-fl y ash system.

Nano-treatment of Autoclaved Aerated Concrete Waste and Its Usage in Cleaner Building Materials

Autoclaved aerated concrete waste(AACW)was used as a raw material to prepare nucleation seed for acceleration of Portland cement.Nano AACW seed with median particle size of 324 nm was prepared by wet grinding method.Both the electrical conductivity and pH value of nano AACW suspension were obviously improved.Both the setting times and intensity of the main hydration heat peak were promoted by nano AACW,indicating the possibility of AACW suspension as nucleation seed.The early age compressive strength before 3 days was also clearly improved by nano AACW,with no negative effect on the late age strength.Furthermore,the reduced CH content with dosage of nano AACW indicates that nano AACW not only plays a role of nucleation seed in cement hydration,but also has a certain pozzolanic reaction.

Utilization of Dredged River Sediment in Preparing Autoclaved Aerated Concrete Blocks

In this study,the dredged river sediment,soft texture and fine particles,is mixed with other materials and transformed into eco-friendly autoclaved aerated concrete(hereinafter referred to as AAC)blocks.The results indicated the bricks produced under the conditions of 30%–34%dredged river sediment,24%cement,10%quick lime,30%fly ash,2%gypsum and 0.09%aluminum powder with 0.5 water to material ratio,2.2 MPa autoclave pressure and 6 h autoclave time,the average compressive strength of 4.5 MPa and average dry density of 716.56 kg/m³were obtained,the two parameters(strength&density)both met the requirement of national industry standard.At the same time,the contents of dredged river sediment,cement,lime,fly ash,gypsum and aluminum powder were 15%,48%,20%,15%,2%and 0.09%,respectively,and the non-AAC block made of 0.5 water to material ratio,the average compressive strength of 3.1 MPa and average dry density of 924.19 kg/m³were obtained,the two parameters(strength&density)also met the requirement of national industry standard.In addition,the AAC block’s phase composition and morphology were micro-analyzed by SEM and XRD,the main substances in AAC block were found to be tobermorite and CSH,Among them,the chemical bond between Si-O-Si and Al-O-Al is broken,Al-O-Si is regenerated,Al substituted tobermorite with better strength is formed,and the compressive strength of AAC is further improved.

Kinetics of Autoclave Curing Process on Autoclaved Aerated Concrete with Magnetite Tailings

Lightweight and energy saving autoclaved aerated concrete(AAC) acting as a newbuilding material were prepared by using magnetite tailings from iron ore as main rawmaterials,and the purpose of comprehensive utilization of tailings resources was to improve their utilization efficiency.The effects of curing system on AAC product performance were discussed.The autoclave curing reaction kinetics was studied as well as the generated amount of hydration product trends over autoclave curing temperature and time were analyzed.The results indicated that the properties of AAC was in accordance with Chinese national standard the A3.5 B06 class of GB/T11968-2006 by prepared from magnetite tailing as the main rawmaterials.Meanwhile,autoclave curing process was controlled by the diffusion velocity through the products ' layers of reactants,and the apparent activation energy of autoclave curing process was 19.269 k J/mol.Compressive strength of aerated concrete is improved by mutual cementation between the appropriate amount of calcium silicate hydrate and tobermorite crystal.

Influence of Polycarboxylic-type Admixture on the Strength of Autoclaved Aerated Concrete

The influence of polycarboxylic-type admixture on the strength of autoclaved aerated concrete（AAC） was investigated. The flexural strength and compressive strength of AAC with polycarboxylic admixture（PA） were tested. The microstructure of AAC reinforced by PA was analyzed using scanning electron microscopic（SEM） methods. The crystal structure analysis of AAC with PA was also carried out using X-ray diffraction（XRD）. The results showed that the compressive strength and flexural strength of AAC were increased by 43.9% and 42.8%, respectively, when 1.5wt% of PA was mixed. In addition, the dosage of admixture influenced the reinforcing effect. Admixture affected pore structure and surface characteristic of the products in autoclaved curing process and improved the formation of high crystallite tobermorite which led to the enhancement of the compressive and flexural strength of AAC.

Autoclaved Aerated Concrete Block Prefabricated Multi-Storey Building Technology

In active response to the national requirements of promoting green building materials and developing prefabricated buildings,it is necessary to continuously optimize and reasonably employ relevant technologies.Autoclaved aerated concrete block prefabricated multi-storey building technology is a new technology,which will not only effectively realize green environmental protection in construction engineering,but also promote the further development of prefabricated buildings.Therefore,this paper analyzes the autoclaved aerated concrete block prefabricated multi-storey building technology for future references.

Flexural behavior of textile reinforced mortar-autoclaved lightweight aerated concrete composite panels

To improve the deficiencies of prefabricated autoclaved lightweight aerated concrete(ALC)panel such as susceptibility to cracking and low load-bearing capacity,a textile-reinforced mortar-autoclaved lightweight aerated concrete(TRM-ALC)composite panel was developed in this study.One group of reference ALC panels and five groups of TRM-ALC panels were fabricated and subjected to four-point flexural tests.TRM was applied on the tensile side of the ALC panels to create TRM-ALC.The variable parameters were the plies of textile(one or two),type of textile(basalt or carbon),and whether the matrix(without textile)was applied on the compression side of panel.The results showed that a bonding only 8-mm-thick TRM layer on the surface of the ALC panel could increase the cracking load by 180%−520%.The flexural capacity of the TRM-ALC panel increased as the number of textile layers increased.Additional reinforcement of the matrix on the compressive side could further enhance the stiffness and ultimate loadbearing capacity of the TRM-ALC panel.Such panels with basalt textile failed in flexural mode,with the rupture of fabric mesh.Those with carbon textile failed in shear mode due to the ultra-high tensile strength of carbon.In addition,analytical models related to the different failure modes were presented to estimate the ultimate load-carrying capacity of the TRM-ALC panels.