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The chemical and mechanical effects of calcium carbonate precipitation for cement-based materials exposed to carbonated brine
International Journal of Greenhouse Gas Control ( IF 3.9 ) Pub Date : 2020-12-08 , DOI: 10.1016/j.ijggc.2020.103221
Zhong-Cun Zuo , Terry Bennett

The present study performs a detailed investigation on the chemical mechanisms of calcium carbonate precipitation for cement-based materials in different reactive environments, which is aiming to interpret the divergences in existing experimental studies. Subsequently, the mechanical influences of carbonation is evaluated for the integrity assessment of wellbore system adopted in the CO2 sequestration. Based on the experimental observation and numerical simulation, the presence of magnesium in the cement leaching system is demonstrated to protect the material from a chemical degradation by sealing the water/cement interface. In the absence of magnesium, the concentration of dissolved CO2 dominates the degradation rate by the pore-clogging effect of the calcium carbonate layer. The interplay of pH and CO2 concentration leads to the dissolution and re-precipitation of calcium carbonate, and consequently presents a shifting Ca-rich layer within the cement matrix. The precipitated calcium carbonate is incorporated with leached cement paste to evaluate the residual elastic moduli by a micromechanical model, which demonstrates that calcium carbonate can counteract the stiffness loss and even rise over the original stiffness. After the dissolution/precipitation of cement constituents, the flexural performance is evaluated with the updated stiffness to demonstrate the influence of carbonation on a cement paste beam. The reinforcement of calcium carbonate layer on the mechanical behaviour gradually is weakening along with the layer shifting inwards, which could further compromise the well integrity.



中文翻译:

碳酸钙沉淀对暴露于碳酸盐水中的水泥基材料的化学和机械作用

本研究对不同反应环境下水泥基材料碳酸钙沉淀的化学机理进行了详细的研究,旨在解释现有实验研究中的分歧。随后,评估碳酸化作用的机械影响,以评估CO 2隔离中采用的井眼系统的完整性。基于实验观察和数值模拟,证明了在水泥浸出系统中存在镁,可以通过密封水/水泥界面来保护材料免受化学降解。在没有镁的情况下,溶解的CO 2浓度通过碳酸钙层的孔堵塞作用,可控制降解速率。pH和CO 2的相互作用浓缩导致碳酸钙的溶解和再沉淀,因此在水泥基质中呈现出富集的富钙层。将沉淀的碳酸钙与浸出的水泥浆混合,以通过微力学模型评估残余弹性模量,这表明碳酸钙可以抵消刚度的损失,甚至可以超过原始刚度。水泥成分溶解/沉淀后,通过更新的刚度评估弯曲性能,以证明碳化对水泥浆梁的影响。随着层向内移动,碳酸钙层对机械性能的增强作用逐渐减弱,这可能进一步损害井的完整性。

更新日期:2020-12-08
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