scholarly journals Effects of Expansive Additives on the Shrinkage Behavior of Coal Gangue Based Alkali Activated Materials

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 816
Author(s):  
Xu Gao ◽  
Chao Liu ◽  
Zhonghe Shui ◽  
Rui Yu
Keyword(s):  
Mechanical Properties ◽  
High Performance Concrete ◽  
Early Stage ◽  
Drying Shrinkage ◽  
Coal Gangue ◽  
Reaction Process ◽  
Activated Coal ◽  
Activated Coal Gangue ◽  
Alkali Activated ◽  
Shrinkage Behavior

The suitability of applying shrinkage reducing additives in alkali activated coal gangue-slag composites is discussed in this study. The effect of sulphoaluminate cement (SAC), high performance concrete expansion agent (HCSA) and U-type expansion agent (UEA) on the reaction process, shrinkage behavior, phase composition, microstructure and mechanical properties are evaluated. The results show that the addition of SAC slightly mitigates the early stage reaction process, while HCSA and UEA can either accelerate or inhibit the reaction depending on their dosage. The addition of SAC presents an ideal balance between drying shrinkage reduction and strength increment. As for HCSA and UEA, the shrinkage and mechanical properties are sensitive to their replacement level; excessive dosage would result in remarkable strength reduction and expansion. The specific surface area and average pore size of the hardened matrix are found to be closely related with shrinkage behavior. SAC addition introduces additional hydrotalcite phases within the reaction products, while HCSA and UEA mainly result in the formation of CaCO3 and Ca(OH)2. It is concluded that applying expansive additives can be an effective approach in reducing the drying shrinkage of alkali activated coal gangue-slag mixtures, while their type and dosage must be carefully handled.

Study on the drying shrinkage of alkali-activated coal gangue-slag mortar and its mechanisms

2019 ◽  
Vol 225 ◽  
pp. 204-213 ◽  
Author(s):  
Ma Hongqiang ◽  
Chen Hongyu ◽  
Zhu Hongguang ◽  
Shi yangyang ◽  
Ni Yadong ◽  
...  
Keyword(s):  
Drying Shrinkage ◽  
Coal Gangue ◽  
Activated Coal ◽  
Activated Coal Gangue ◽  
Alkali Activated

Shrinkage-reducing measures and mechanisms analysis for alkali-activated coal gangue-slag mortar at room temperature

2020 ◽  
Vol 252 ◽  
pp. 119001 ◽  
Author(s):  
Hongqiang Ma ◽  
Hongguang Zhu ◽  
Hongyu Chen ◽  
Yadong Ni ◽  
Xiaonan Xu ◽  
...  
Keyword(s):  
Room Temperature ◽  
Coal Gangue ◽  
Activated Coal ◽  
Activated Coal Gangue ◽  
Alkali Activated

Study of Complex Chemical Activator on Activation Effect of Calcined Coal Gangue

2012 ◽  
Vol 450-451 ◽  
pp. 832-835 ◽  
Author(s):  
Xu Yan Song ◽  
Jing Yun Han ◽  
Zhi Hai Gao
Keyword(s):  
Mechanical Properties ◽  
Physical And Mechanical Properties ◽  
Coal Gangue ◽  
Activation Effect ◽  
Complex Chemical ◽  
Mortar Strength ◽  
Activated Coal ◽  
Cement System ◽  
Activated Coal Gangue ◽  
Chemical Activator

Three kinds of complex chemical activators were prepared and then introduced into calcined coal gangue cement. Physical and mechanical properties such as mortar fluidity and mortar strength and shrinkage were tested. The results can show that: excitation effects of multiple complex chemical activators may obvious, where with 8% of J1, 50% of cement replaced with activated coal gangue, compressive strength of the system at ages of 28 days can reach 40.7MPa. Compared with coal gangue cement system without exciting agent, in calcined coal gangue cement system with complex activators early shrinkage increased obviously and later shrinkage may be equivalent to that of pure cement.

Study on compressive strength and durability of alkali-activated coal gangue-slag concrete and its mechanism

2020 ◽  
Vol 368 ◽  
pp. 112-124 ◽  
Author(s):  
Hongqiang Ma ◽  
Hongguang Zhu ◽  
Chao Wu ◽  
Hongyu Chen ◽  
Jianwei Sun ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Coal Gangue ◽  
Activated Coal ◽  
Strength And Durability ◽  
Activated Coal Gangue ◽  
Alkali Activated

Immobilization of uranium soils with alkali-activated coal gangue–based geopolymer

2021 ◽  
Author(s):  
Shukui Zhou ◽  
Jiali Li ◽  
Lishan Rong ◽  
Jiang Xiao ◽  
Yingjiu Liu ◽  
...  
Keyword(s):  
Coal Gangue ◽  
Activated Coal ◽  
Activated Coal Gangue ◽  
Alkali Activated

scholarly journals Study of Mechanical Properties and Durability of Alkali-Activated Coal Gangue-Slag Concrete

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5576
Author(s):  
Hongguang Zhu ◽  
Sen Yang ◽  
Weijian Li ◽  
Zonghui Li ◽  
Jingchong Fan ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Damage Mechanics ◽  
Ordinary Portland Cement ◽  
Coal Gangue ◽  
Function Model ◽  
Freeze Thaw ◽  
Activated Coal ◽  
Activated Coal Gangue ◽  
Alkali Activated

Herein, a new geopolymer is recognized as a potential alternative cementing material of ordinary Portland cement (OPC), which is used for reducing carbon emissions and efficiently recycling the waste. Therefore this paper mainly studied the alkali-activated coal gangue-slag concrete (ACSC) was prepared by using the coal gangue-slag and Na2SiO3 and NaOH complex activator. The ratio of coal gangue (calcined and uncalcined) coarse aggregate replacing the gravel was 0%, 30%, 50%, 70%, and 100%. The water and salt freeze-thaw resistance, compressive strength, chloride permeation, microstructure, performance mechanism, inner freeze-thaw damage distribution, and mechanics models of ACSC were investigated. Results show that ACSC displayed excellent early age compressive strength, and the compact degree and uniformity of structure were better compared with the ordinary Portland cement (OPC) when the coal gangue replacement rate was less than 50%. The ACSC demonstrated the best chloride penetration resistance under 30% uncalcined coal gangue content, which was less than 27.75% lower than that of using OPC. At the same number cycles, especially in the salt freezing, the calcined coal gangue had lowered advantages of improving resistance freeze-thaw damage resistance. Water and salt accumulative freeze-thaw damage mechanics models of ACSC were established by using the relative dynamic elasticity modulus. The exponential function model was superior to the power function model with better precision and relativity, and the models accurately reflected the freeze-thaw damage effect.

scholarly journals Experimental Study on the Characteristics of Activated Coal Gangue and Coal Gangue-Based Geopolymer

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2504
Author(s):  
Weiqing Zhang ◽  
Chaowei Dong ◽  
Peng Huang ◽  
Qiang Sun ◽  
Meng Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Activation ◽  
Amorphous Structure ◽  
Coal Gangue ◽  
Lower Amount ◽  
Activation Temperature ◽  
Microstructure Changes ◽  
Thermally Activated ◽  
Activated Coal ◽  
Activated Coal Gangue

Coal gangue-based geopolymer (CGGP) is one of the hot spots existing in the recycling of coal gangue resources due to its good comprehensive mechanical properties. However, the coal gangue structure is stable and reactivity is poor, so the coal gangue needs to be activated before utilization. In this paper, the microstructure changes of activated coal gangue by different mechanical and thermal activation methods, as well as the mechanical properties and microstructure changes of the CGGP specimens were studied by experimental investigation. The results indicated that mechanical activation and thermal activation were two effective methods to change the reactivity of coal gangue, which consisted of destroying the stable kaolinite structure and improving the activity of coal gangue. Conversely, part of the amorphous structure in coal gangue was destroyed when the activation temperature reached 900 °C, which was not conducive to the further enhancement of coal gangue activity. For the CGGP prepared by thermally activated coal gangue and modified sodium silicate alkali solution, the uniaxial compressive strength of the CGGP specimens decreased with thermal activation temperatures of the raw coal gangue materials at 700 °C, 800 °C, and 900 °C. The main reason for this was the lower amount of the active metakaolin structure in coal gangue at 900 °C, which was not conducive to the geopolymerization process.

scholarly journals Preparation and Reaction Mechanism Characterization of Alkali-activated Coal Gangue–Slag Materials

Materials ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2250 ◽  
Author(s):  
Hongqiang Ma ◽  
Hongguang Zhu ◽  
Cheng Yi ◽  
Jingchong Fan ◽  
Hongyu Chen ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Sodium Hydroxide ◽  
Energy Dispersive Spectrometer ◽  
Coal Gangue ◽  
Influential Factor ◽  
Raw Material ◽  
Activated Coal ◽  
Activated Coal Gangue ◽  
Alkali Activated ◽  
Slag Content

In this paper, slag is used as a calcium source to make alkali-activated coal gangue–slag (AACGS) based material. The reaction mechanism of AACGS materials was discussed in depth by means of XRD, FT-IR, 29Si MAS-NMR (nuclear magnetic resonance) and SEM-EDS (energy dispersive spectrometer). The experimental results show that coal gangue can be used as a raw material for preparing alkali-activated materials. The liquid–solid ratio is the most influential factor on AACGS paste fluidity and strength, followed by slag content. As the modulus of sodium hydroxide increases, the depolymerization process of the reactant precursor is accelerated, but the high sodium hydroxide concentration inhibits the occurrence of the early coal gangue–slag polycondensation reaction, and exerts little effect on the 28 d compressive strength. Ca2+ in the slag promotes exchange with Na+, and the product is converted from N-A-S-H gel to C-(A)-S-H gel, and C-(A)-S-H is formed with higher Ca/Si ratio with the increase of slag content. The slight replacement of coal gangue by slag can greatly improve the reaction process and the strength of AACGS materials.

scholarly journals Experimental Study of the Mechanical and Microstructure Characteristics of Coal Gangue Road Stabilization Materials Based on Alkali Slag Cementation

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3601
Author(s):  
Changbai Wang ◽  
Junxin Yang ◽  
Shuzhan Xu
Keyword(s):  
Compressive Strength ◽  
Unconfined Compressive Strength ◽  
Coal Gangue ◽  
Hydration Time ◽  
Alkali Activated Slag ◽  
Microstructure Characteristics ◽  
Activated Coal ◽  
Activated Slag ◽  
Activated Coal Gangue ◽  
Alkali Activated

To accelerate the resource utilization of coal gangue and meet the strategic requirements of carbon neutralization, alkali-activated, slag-cemented coal gangue is applied in the preparation of solid waste-based road stabilization materials. Here, the cementation characteristics and microstructure characteristics of alkali-activated, slag-cemented coal gangue road stabilization materials are studied using the alkali equivalent and coal gangue aggregate ratio as experimental variables. The results show that with the increase in alkali equivalent from 1% to 7%, the unconfined compressive strength of the alkali-activated coal gangue road stabilization material initially increases and then decreases, with 3% being the optimal group in terms of stabilization, the aggregate ratio of coal gangue increases from 70% to 85%, and the 7-day unconfined compressive strength of the stabilized material decreases approximately linearly from 8.16 to 1.68 MPa. At the same time, the porosity gradually increases but still meets the requirements of the specification. With the increase in hydration time, a large number of hydration products are formed in the alkali slag cementation system, and they are closely attached to the surface of and interweave with the coal gangue to fill the pores, resulting in the alkali slag slurry and coal gangue being brought closer together.

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