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Present study aims to explore the effect of sintering temperature and dwelling time on the characteristics and morphological structure of lightweight aggregates made from dry sewage sludge and waste glass powder. The mixtures were sintered at temperatures from 1100 °C to 1200 °C at a heating rate of 10 °C/min with a dwelling time of 10, 20, and 30 min to produce lightweight aggregate samples. The thermophysical behavior of the mixtures and the physic-mechanical properties (including water absorption, particle density, and compressive strength) of the obtained lightweight aggregates were studied. The microstructure of the lightweight aggregates was also analyzed using X-ray micro-computed tomography. Results indicate that increasing the sintering temperature or extending the dwelling time will reduce the particle density and compressive strength of lightweight aggregates. Moreover, the sintering temperature and dwelling time show a considerably influence on the pore structure of lightweight aggregates, which is strongly related to the physical characteristics of the lightweight aggregates. The lightweight aggregates obtained at optimized sintering temperature of 1180 °C with an optimal dwelling time of 10 min show water absorption of 1.01%, particle density of 0.78 g/cm3, and compressive strength of 7.10 MPa, thereby meeting the standard requirement of GB/T 17431.2–2010.

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.

In this paper, rice husk ash (RHA) with different average pore diameters and specific surface areas was used to replace 10% slag in the preparation of alkali-activated slag (AAS) pastes. The effect of RHA addition on the shrinkage, hydration, and strength of AAS pastes was studied. The results show that RHA with a porous structure will pre-absorb part of the mixing water during paste preparation, resulting in a decrease in the fluidity of AAS pastes by 5–20 mm. RHA has a significant inhibitory effect on the shrinkage of AAS pastes. The autogenous shrinkage of AAS pastes decreases by 18–55% at 7 days, and the drying shrinkage decreases by 7–18% at 28 days. This shrinkage reduction effect weakens with the decrease in RHA particle size. RHA has no obvious effect on the type of hydration products of AAS pastes, whereas RHA after proper grinding treatment can significantly improve the hydration degree. Therefore, more hydration products are generated and fills the internal pores of the pastes, which significantly improves the mechanical properties of the AAS pastes. The 28 day compressive strength of sample R10M30 (the content of RHA is 10%, RHA milling time is 30 min) is 13 MPa higher than that of blank sample.

Four cellulose ethers (CEs) were compared for their effects on the pore structure of cement paste using mercury intrusion porosimetry. The experimental results show that the total pore volume and porosity of cement pastes containing the four cellulose ethers are significantly higher than that of the pure cement pastes and the total pore volume and porosity of cement pastes containing HEC (hydroxyethyl cellulose ether) or low viscosity cellulose ethers are low in four CEs. By changing the surface tension and viscosity of liquid phase and the strengthening of liquid film between air voids in cement pastes, CEs affect the formation, diameter evolution and upward movement of air voids and the pore structure of hardening cement paste. For the four CEs, the pore volume of cement pastes containing HEC or low viscosity cellulose ethers is higher with the diameter of 30–70 nm while lower with the diameter larger than 70 nm. CEs affect the pore structure of cement paste mainly through their effects on the evolvement of the small air voids into bigger ones when the pore diameter is below 70 nm and their effects on the entrainment and stabilization of air voids when the pore diameter is above 70 nm.

The objective of this study was to assess the feasibility of application of municipal solid waste incineration (MSWI) bottom ash as a substitute of quartz sand for the preparation of autoclaved aerated concrete (AAC). Influence of substitution mass ratio and fineness of MSWI bottom ash on the physical-mechanical properties and microstructure of AAC was investigated. Leaching toxicity was also determined to ensure the environmental safety of AAC with MSWI bottom ash. The results demonstrated that the incorporation of MSWI bottom ash can reduce the gas-foaming time, compressive strength, density and thermal conductivity. Moreover, compressive strength and density of AAC increase with the increasing of fineness of MSWI bottom ash. The reactive silica in the bottom ash strongly affected the formation of tobermorite. The needle-like tobermorite in the control sample was transformed into plate-like tobermorite with the increase of bottom ash up to 40% and the crumbled foiled tobermorite and grass-like C-S-H structure formed in ACC with 100% bottom ash. It is also evident that heavy metal concentrations in the leachates of AAC and autoclaved water are far lower than recommended in the GB5085.3-2007.

Generally, bleeding and segregation can be solved with addition of hydroxypropyl-methyl cellulose ether (HPMC) in real concrete. However, the negative effect of this on dispersion of polycarboxylate superplasticizer (PCE) can always be found. In order to deeply understand this negative effect, the rheology of cement paste in the presence of PCE and HPMC was investigated, and the mechanism behind the interaction between PCE and HPMC was revealed with total organic carbon analyzer, X-ray photoelectron spectrometer and dynamic light scattering. The results show that addition of HPMC can obviously increase the plastic viscosity and yield stress of cement paste plasticized by PCE, showing negative effect on fluidity. One reason for this negative effect is that HPMC can be combined with Ca2+ in pore solution, resulting in agglomeration and even precipitation, which can consume and invalid PCE; another reason is that HPMC can perturb the adsorption of PCE to exert dispersion by competitive adsorption. By contrast, much stronger negative effect can be observed with greater molecular weight of HPMC. It is inferred that proper molecular weight of HPMC can balance the negative effect of HPMC on dispersion of PCE and the viscosity-enhancing effect of HPMC to improve bleeding and segregation. Such results were expected to provide guidance on the use of HPMC to optimize workability of cement-based materials plasticized by PCE in real engineering practice.

Alkali-activated slag (AAS) attracted wide attention in low carbon cementitious materials. In this study, superfine slag was activated by sodium carbonate (SC), and marble powder (MP) was also used. The effect of MP on SC-activated slag binders were investigated in terms of fluidity, compressive strength , hydration heat and microstructure analysis. Additionally, carbon emissions of the binders were evaluated. Results showed that the compressive strength of SC-activated slag mortars was decreased with the addition of MP, but the strength was still at an acceptable level. The 7-day and 28-day strength of 5 % Na 2 O-E activated slag mortars was 52.0 MPa and 64.7 MPa, while that of the mortars containing 30 % MP was 21.9 MPa and 51.0 MPa, with an obvious decrease. The main hydration products of SC-activated slag/MP pastes were C-A-S-H, calcite, hydrotalcite and gaylussite, and MP seemed no hydration activity in this system. Moreover, carbon emissions of SC-activated superfine slag/MP binders were 104–126 kg CO 2-e/t, and it seemed much lower than that of strong bases-activated slag system. Such results indicated that this kind of binders had great potential in low carbon cementitious materials.

In this study, nano cement particles (Nano-C) were prepared via wet grinding cement. Nano-C was characterized by laser particle size distribution, X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Scanning electron microscope (SEM), Transmission electron microscope (TEM) and 29Si magic-angle spinning nuclear magnetic resonance (29Si MAS NMR). The particle size of Nano-C was D50 = 53.1 nm. In order to disperse the nano particles, polycarboxylate superplasticizer was used in the process of grinding. The results show that 0.5%, 1.0%, 2.0%, and 4.0% Nano-C could increase the 12-h compressive strength by 49%, 109%, 194% and 197%, in comparison with the reference. The influence of Nano-C on the hydration, hydration products, microstructure was tested by means of hydration heat, chemical shrinkage, XRD, Thermogravimetric analysis (TGA), SEM, 29Si MAS NMR, and Mercury injection porosimetry (MIP). The results revealed that Nano-C not only used as distinguished nucleus seed to enhance the PC system hydration but also exhibited high hydration activity to produce C-S-H gel to further raise the PC hydration up. These findings provided a novel way to prepare nanomaterials, which was expected to provide a way to improve the early strength of precast concrete.

The high annual output and low utilization rate of flue gas desulfurization (FGD) gypsum cause acute damage to the environment in China. FGD gypsum board is a potential product, but its wide application is limited due to its poor mechanical properties and water resistance. Here, anhydrous calcium sulfate whisker (ACSW) and calcium carbonate whisker (CW) were chosen to improve the properties of FGD gypsum. The effects of two types of whiskers on the working performance, mechanical properties, and water resistance of FGD gypsum were analyzed and compared. The results show that the incorporation of whiskers reduced the processability of the FGD gypsum slurry. The mechanical properties of FGD gypsum improved greatly because the whiskers can increase the contact points between the crystals and fill the pores in FGD gypsum. The 7-day dry flexural strength of FGD gypsum with ACSW and CW increased by 46.99% and 33.07%, respectively. ACSW was better for enhancement than CW due to its good adhesion with gypsum. However, ACSW was not as effective as CW in improving the water resistance, because the structure of ACSW will be destroyed in a humid environment. This research focuses on improving the mechanical and further utilization of FGD gypsum, which also provides a theoretical basis for improving the performance of FGD gypsum.

Polymer-modified cement-based materials (PMC) have been widely applied in civil construction and municipal projects. In order to obtain deeper insight into the workability of PMC, the effect of polyacrylic acid emulsion (PAE) on fluidity of cement paste was investigated in this study. The fluidity was assessed with mini slump, and the change of Ca 2+ concentration in pore solution was tested with inductive coupled plasma emission spectrometer. Zeta potential and adsorption behavior were characterized to reveal the mechanism behind the fluidity results. The results show that the effect of PAE on fluidity depends on the added dosage: dosage less than 5.0% reduces the fluidity, while the opposite is true with dosage more than 5%, which can also be indicated from the change of Ca 2+ concentration in pore solution. Conductivity and X-ray photoelectron spectrometer (XPS) results demonstrate the chemical adsorption of PAE on the surface of cement particles. Dynamic light scattering (DLS) results strongly prove that the surface group of the PAE used is SO 3 − rather than COO − . Finally, the dispersion model was proposed to illustrate mechanism behind: with a small amount of PAE, the decline in zeta potential caused by adsorption of negatively charged PAE and the agglomeration of cement particles caused by electrostatic attraction of PAE are responsible for the reduced fluidity; while with a great amount of PAE, the negatively increased zeta potential, lubrication effect provided by non-adsorbed PAE, and filling effect of PAE are the main reason for the increased fluidity. Such results would give deeper understanding about the effect of polymer emulsion on rheology of cement paste.

Due to tendency of agglomeration in the nano-size scale, dispersion of silica nanosphere is of great importance for its application in aqueous phase system. In this paper, silica nanosphere was prepared by sol–gel method, followed by an immediate in-situ surface modification with siloxane-coupled polycarboxylate dispersants through a one-pot method. The particle size, surface topography, and chemical composition were analyzed by scanning electron microscopy, energy dispersive spectrometer, thermal gravimetry, and sedimentation test. For samples modified by siloxane-coupled polycarboxylate with concentration up to 3 wt%, the particle size decreased and monodispersity of the size increased, suggesting siloxane-coupled polycarboxylate have a size regulation effect on particle growth of silica nanosphere. Thermal gravimetry and energy dispersive spectrometer results confirmed that the dispersant strongly absorbed on the growing surface of silica nanosphere even after ultrasound cleaning and the absorbed amount increase with dispersant concentration for these samples. Compared with unmodified samples that completely precipitated after standing for 10 days, dispersion stability of modified samples in aqueous solution increased with dispersant solution content of up to 3 wt%. Interestingly, when siloxane-coupled polycarboxylate content increased to 5 wt%, particle size reverts back to larger size and the size dispersity increased which is due to decrease of dispersant absorption amount. The reverse behavior of higher dispersant concentration could be well explained by formation of dispersant micelles or oligomers, which indicates that there is an optimum modification concentration.

Sulphoaluminate cement (SAC) is increasingly attracting the attention of academic and industry researchers, not only because of its fast setting and high early strength, but also due to the low CO 2 emissions and low preparation temperature. The fast setting also results in poor workability. Generally, this problem can be improved by incorporation of retarders. However, it is often ignored that these retarders may obviously affect the plasticizing effect of superplasticizer by competitively adsorbing onto the surface of the cement particles. In this study, the effect of borax on rheology of SAC paste with polycarboxylate superplasticizer (PCE) has been investigated to gain deeper insight into competitive adsorption. The rheology was characterized with mini slump and rotor rheometer. Adsorption behavior was studied with total organic carbon analyzer and inductive coupled plasma emission spectrometer. The surface performance of cement grains was discussed with X-ray photoelectron spectrometer and scanning electron microscopy. Dispersion model was then proposed to illustrate the mechanism behind the difference in rheology. The results show that borax can be precipitated with Ca 2+ in the immediate vicinity of cement particles to adsorb onto the surface of cement grains and form a calcium-based borate layer on the surface, which is responsible for the retarding effect and plasticizing effect of borax. Competitive adsorption would take place between PCE and borax, and this would tend to reduce adsorption amount of PCE and reduce the dispersion. The dispersion of PCE-borax system in SAC depends on the dosage of borax: a small amount of borax would increase the dispersion, mainly because the retarding effect and plasticizing effect of borax predominate; while a large amount of borax would reduce the dispersion, because the competitive adsorption effect becomes predominant. It is expected that these results would provide the useful experience for the application of PCE and borax in high fluidity SAC paste in real engineering practice.

The feasibility of recycling contaminated soil by preparing artificial fine aggregate (AFA) and applying in artificial fine aggregate mortars (AFAM) was investigated systematically. Properties and heavy metal immobilization status of AFA, compressive strength and heavy metal leaching behavior of AFAM were tested. Results showed that Cu reduced the melting and crystallization temperatures of AFA, whereas Cr improved that. Heavy metal addition had a negative impact on the compressive strength of AFAM, but the toxicity characteristic leaching procedure (TCLP) test indicated that the AFAM system was is suitable for solidification of heavy metals. Moreover, it was observed that Cu leaching almost disappeared in the initial periods, while it tended to dissolve in the terminal periods. The leaching mechanism of AFAM with Cr at the initial periods conformed to Fick's law of diffusion, and it tended to deplete in the terminal periods. These results are practically instructive the recycling of heavy metal contaminated solid waste in the field of construction materials.

Turmeric residue, a solid waste discharged from the curcuminoids industry, is difficult to recover due to high concentrations of strong acids, organic solvents, and plant fibers. In this study, organic turmeric residue was used as the main raw material for the preparation of ceramic foam, in comparison with inorganic granite scraps. The bulk density, compressive strength, and thermal conductivity of ceramic foam were evaluated. And the microstructure, phase assemblage, and reaction at the high temperature were respectively characterized by computed tomography, X-ray diffraction, thermal analysis. The results revealed that the addition of turmeric residue was conducive to the formation of pore and the generation of amorphous glass phase, thereby improving the lightweight, mechanical performance, and thermal insulation. This study would provide a new perspective for the utilization of turmeric residue and the preparation of ceramic foam.

Owing to the insufficient application of recycling methods, the overall amount of coal gangue (CG) has been increasing at a high rate in China. Therefore, development of an efficient method for the CG reuse in other fields has become a pressing issue. This study aims to discover an effective method for implementing an autoclaved process for the preparation of environmentally friendly and lightweight building materials, such as autoclaved aerated concrete (AAC), with the goal of reusing solid waste and reducing the environmental hazard associated with high-calcium coal gangue (HCCG). The chemical composition of HCCG before and after the treatment was analyzed. The effects of the substitution amount and fineness of HCCG on the physical-mechanical properties and hydration products of the AAC were studied. The results show that the incorporation of HCCG does not affect the slurry performance, a vital element in gas foaming, owing to its contribution to the heat and alkalinity of slurry. Moreover, with increasing HCCG content, both, the bulk density and compressive strength of the AAC increased; the best mix contained 8% cement, 58% HCCG, 31% sand, and 3% gypsum (corresponding to 599.4 kg/m3 and 4.57 MPa). These characteristics were in good compliance with the requirements on AAC blocks GB 11968-2006 for B06, A3.5. In addition, an assessment of the safety associated with using HCCG in AAC was conducted, revealing that high-calcium coal gangue autoclaved aerated concrete (HCCG-AAC) can be regarded as a nonhazardous building product and the proposed autoclaved curing can actually solidify heavy metals. Finally, the favorable influence of using high-volume HCCG waste was discussed from the economic viewpoint, which indicates that using HCCG lowers the cost by 40%. The results of this study can provide a new resource utilization method for solid waste coal gangue; in addition, this study can also be used as a theoretical basis for the preparation of autocalved aerated concrete with other low-calcium gangue or solid waste.

With the objective of reducing the negative impacts on environment and utilizing the secondary resource of tailings, the possibility of preparing AAC by using iron tailing was investigated. The bulk density and compressive strength were determined to indicating the feasibility of preparing AAC blocks from iron tailing. The morphology (FESEM-EDX), mineral constituent (XRD), thermal characteristics (TG-DSC) and crystal characteristics (29Si-NMR) of hydration products of AAC samples were analyzed to demonstrate the hydration characteristics of AAC products containing iron tailings effected by iron tailing content and fineness. The results indicated that the increasing content of iron tailing has negative effect on the mechanical property of AAC, and the finer of iron tailings can effectively enhance strength of AAC blocks. The main minerals in AAC products are C-S-H gel, tobermorite, anhydrite, hydrogarnet, and some residual minerals including quartz and calcite accompanied by ferric oxide and white mica in minor quantities. The increasing content of iron tailing obviously reduces the amount of calcium silicate hydrates; meanwhile, the finer of iron tailing accelerated the decomposition of white mica during the autoclaving process and has slight negative effect on crystallinity of tobermorite. It was also suggested that Al and Mg ions in iron tailings got into the structure of tobermorite during the hydrothermal reaction. This study provided the theoretical foundation for the utilizing of iron tailings in AAC production.

Sodium tripolyphosphate (STPP) is usually employed as an auxiliary material in superplasticizer system, because the presence of STPP in superplasticizer system can significantly improve the workability of the fresh concrete. Generally, the retarding effect of STPP on cement hydration can obviously delay the formation of hydration products and cut down the consumption amount of free water and superplasticizer at the very beginning, which is accepted as the main reason for the enhanced dispersing ability of the superplasticizer system. However, the adsorbing behavior, not only including the adsorption amount but also the thickness of adsorption layer, is of great importance to the performance of polycarboxylate superplasticizer (PC). The aim of the paper is to explain why the presence of STPP can obviously enhance the initial dispersing ability of PC system from the point of view of adsorbing behavior. Specifically, adsorption amount of PC and STPP in PC-STPP system was tested with the Total Organic Carbon analyzer (TOC) and Inductive Coupled Plasma Emission Spectrometer (ICP); the thickness of adsorption layer was analyzed with X-ray photoelectron spectroscopy (XPS). The adsorption models were then proposed to reveal the relationship between the adsorbing behavior and the dispersing ability. The result shows that in STPP single system, the multiple-adsorption layer formed by STPP and Ca 2+ are inferred to be the main reason for the excellent retarding effect. In PC-STPP system, adsorbing ability of STPP is considerably stronger than that of PC, which results in the preferential adsorption of STPP; the multiple-adsorption layer containing several layers of STPP inside and a PC layer outside is inferred responsible for the thicker adsorption layer than that of the single system PC. The results also suggest that the dispersing ability of the multicomponent superplasticizer system with the retarder is closely related to the thickness of adsorption layer rather than the superficial adsorption amount.

Based on the background that a large amount of iron tailings was stockpiled in China, the most appropriate preparation conditions of producing autoclaved aerated concrete (AAC) with iron tailing was studied. The slurry properties were tested to evaluate the effects of the raw material factors on gas forming character. The compressive and specific strengths were measured to assess the feasibility of producing B05, A2.5 AAC blocks. The analysis of morphology, mineral components and thermal property were carried out in order to determine the mineral composition of iron tailing AAC blocks. Leaching toxicity was determined to ensure the environmental safety of iron tailing AAC blocks. The results shows that under the following conditions, cement 8%, quicklime 21%–27%, 20 min ball milled siliceous 62%–68% (with 40%–60% substituted by iron tailings), gypsum 3%, ratio of water to raw material (W/R) 0.6, aluminum (Al) powder 0.14% and at 1.4 MPa steam pressure maintaining for 8 h, the bulk density can be between 490 and 525 kg/m 3 , compressive strength higher than 2.5 MPa and specific strength higher than 4700 N m/kg. The main minerals in the AAC were dough-like CSH gel, flake-like tobermorite and long-strip anhydrate besides quartz and other residual minerals from the iron tailings. The compressive strength is mainly attributed to the interconnected microstructure constituted of CSH gel and tobermorite. The thermal analysis also proved the existing of the main minerals.

The semi-carbonization method is a kind of waste treatment to carbonize rice straw fiber at low semi-carbon temperature. The rice straw fiber is carbonized incompletely, which serves as building materials additive. The results reveal that the optimized carbonization condition is at 313 °C for 20-40 min with H3PO4 as activator. The structure of semi-carbonized straw fiber displays a large quantity of micropores, with which the wall thickness and the pore diameter are in the range of 1-4 μm, presenting the iodine sorption value of 1 320-1 470 mL/g and the methylene blue sorption value of 1 330-1 460 mg/g, respectively. Moreover, the acidic oxygen-containing groups impart the structure higher sorption of polar molecules. The semi-carbonized rice straw fiber with open and closed micro-mesopores demonstrates good hygroscopicity, implying the potential application as a functional additive in building materials.

Phosphogypsum is the by-product of phosphate of fertilizer or phosphate which causes serious environmental pollution. In this work, a series of phosphogypsum whiskers were prepared using phosphogypsum as raw materials and NH4Cl as additive through the atmospheric water solution method. The results showed that the ammonium chloride solution has a great influence on phosphogypsum whiskers growth and the solubility. The best whisker aspect ratio of phosphogypsum was preferred in 1 mol/L NH4Cl solution, in which the solubility achieved 6.434 mg/mL and the aspect ratio reached 69.29. Besides, NH4Cl was found to have a modified effect on gypsum whiskers’ growth and it can be used to get mesh or dendritic whiskers.

This paper presents a study on the feasible utilization of municipal sewage sludge (SS) and waste glass (WG) powder for the production of lightweight aggregates (LWAs). Mixtures with different WG contents (0%, 5%, 10%, 15%, and 20%) were sintered at 1180 °C with heating rate of 10 °C/min and a dwelling time of 20 min to obtain LWAs samples. The thermophysical behavior of the mixtures was examined through TG-DTA and fusibility tests. The physic-mechanical properties of the obtained LWAs including water absorption, particle density, and compressive strength were studied. The phase compositions and microstructure of the LWAs were analyzed by SEM-EDS, XRD, and micro-CT. Results indicated that adding an appropriate amount of WG contributed to the bloating of SS and to the production of LWAs with high porosity and proper mechanical property. LWAs containing 10% WG and sintered at 1180 °C for 20 min showed a particle density of 0.76 g/cm3, water absorption of 0.87%, and compressive strength of 6.48 MPa, thereby meeting standard requirement of GB/T 17431.2–2010. The obtained LWAs also showed uniform pore-volume distribution.

In order to avoid environmental pollution from copper tailings (CT), this paper presented a study on potential utilization of CT in the preparation of low heat cement clinker (LHC). The effect of CT addition on the properties of LHC was investigated by using free lime (f-CaO) content test and X-ray diffraction (XRD). Furthermore, to study the hydration properties of LHC paste, the produced LHC samples were mixed with 0.37 wt% gypsum to prepare the LHC paste at a water/binder ratio of 0.30. The compressive strength, hydration process, hydration products of LHC paste and solidification of heavy metals in LHC and the hydrated paste were analyzed. The experimental results showed that CT can be used as a raw material for LHC production. The CT is beneficial for the formation of 2CaO•SiO2 (C2S) during the sintering process of LHC. Furthermore, LHC paste with higher CT addition showed lower hydration heat during the first 7 d hydration. With 2 wt% CT added, the hydration of LHC paste can be promoted and the compressive strength was higher than the blank group at the age of 60 d. The leaching tests indicated that heavy metals in CT can be stabilized in LHC and LHC paste during the sintering process and the hydration process.

Zinc-contaminated soil is hazardous waste due to the presence of a quite high level of heavy metal zinc. If disposed improperly, it will pose a severe threat to the environment and human health. In order to avoid environmental pollution from the heavy metal zinc in contaminated soil, this study focused on the assessment of the feasibility of using zinc-contaminated soil in the production of lightweight aggregate (LWA) and its effect on solidification of zinc. The LWA produced from the contaminated soil have reached the required standard of LWA, and the zinc was beneficial for the expansion of LWA during the sintering process. The solidification rate of zinc was calculated by a formula defined as a ratio of the content of solidified zinc to the total zinc content in LWA. The results indicated that the zinc can be stabilized as Zn2SiO4 and ZnFe2O4, and the solidification rate of zinc in all of the LWA samples was greater than 99.9%. Furthermore, a prolonged leaching test showed that the leaching concentrations of zinc were much lower than the safety limit in accordance with the Chinese standard set to identify the safety of the material according to leaching concentrations of heavy metals. These findings contribute to the mechanistic understanding of the solidification of zinc in the LWA produced from contaminated soil. Meanwhile, this cleaner production technique for LWA will contribute to the sustainable manufacture of LWA.

This paper aims to solve the problem of high water absorption in the use of circulating fluidized bed combustion ash. Meanwhile, the feasibility of using the circulating fluidized bed combustion ash to prepare autoclaved aerated concrete was studied. The circulating fluidized bed combustion ash autoclaved aerated concrete samples with different water consumption and different dosages of water reducing agent were prepared. The rheological properties and gas-foaming results of the slurry, the compressive strength, the dry density, specific strength, pore structure and hydration products of the products were analyzed. The results show that the incorporation of polycarboxylate superplasticizers has a positive effect on the rheological properties of the slurry, the gas generation, and the physical properties of the sample. Its water reducing effect not only can improve the rheological properties of the slurry to match the gas generation rate of the aluminum powder, but also optimize the pore structure to reduce the number of harmful pores (less than 50 nm) and improve the strength of the product. Because a large number of uneven macropores are introduced, the high water consumption is unfavorable to the compressive strength of the product to a certain extent. However, too low water consumption would hinder cement hydration to produce C-S-H gel and reduce the formation of tobermorite. It is noticed that the reasonable combination of water consumption and water reducing agent can improve the strength of aerated concrete products without significantly changing the bulk density of the sample. This paper provides a theoretical basis for use of other high-water-demand solid wastes similar to circulating fluidized bed fly ash in the preparation of autoclaved aerated concrete.

High-fluidity gypsum-based materials have been widely used in grouting materials, self-leveling floors, wall materials, and three-dimensional (3D) printing materials. High fluidity means ex...

Clay reduces fluidity and increases fluidity loss of concrete added with polycarboxylate superplasticiser. Sometimes it cuts down concrete durability. Fluidity of clay–cement paste with the addition of polycarboxylate superplasticiser, adsorption amount of polycarboxylate superplasticiser and ζ-potential has been tested to understand the effect of polycarboxylate superplasticiser on cement–clay systems. The results show that cement particles have a smooth surface; there are lots of layered or sheet structure existing on the surface of clay; when the particle size distribution is little different, the specific surface area of clay is 17 times that of cement; it is the reason why polycarboxylate superplasticiser adsorption on clay is much greater than that of cement. Initial adsorption amount and equilibrium adsorption amount of polycarboxylate superplasticiser on clay are 3–4 times that of cement; strong PC adsorption of clay is the main reason why the presence of clay reduces fluidity and increase...

Polycarboxylate superplasticizer (PCE) is widely employed in cement-based material to reduce water demand and increase fluidity, and even to improve durability of concrete. Generally, aggre...

Phosphate is usually considered as an excellent retarder in cement-based materials. It is often thought that the mechanism behind this excellent retarding effect is attributed to the precip...

By means of thermogravimetric analysis (TGA), influences of organic acids such as citric acid, oxalic acid and tartaric acid on decomposition process and thermal behaviors of calcium carbonate were investigated in non-isothermal condition. Experiments were conducted from the ambient temperature to 1273 K at a heating rate of 10 K min −1 . Moreover, the kinetic parameters (activation energy and pre-exponential factor) of the mixtures of calcium carbonate and organic acids were determined using the Coats–Redfern method. It is indicated that the decomposition process of calcium carbonate containing different organic acids includes three or four weight loss processes. In the zone of 370–450 °C, energy is released due to the combustion of organic products decomposed from organic salts, and energy increases with the increase of molecular weight of organic acid. Activation energy of the samples containing citric acid, oxalic acid and tartaric acid is decreased by 34.9%, 28.8% and 31.9%, respectively. The results may be used to provide a useful basis for further applying industrial wastes containing different organic acids in cement industries with high-efficiency.