Alkali-aggregate reaction in recycled aggregate concrete

Peng, Ziyi; Shi, Caijun; Shi, Zhenguo; Lu, Bao; Wan, Shu; Zhang, Zuhua; Chang, Jun; Zhang, Tingting

doi:10.1016/j.jclepro.2020.120238

Cited by 63 publications

(12 citation statements)

References 58 publications

(119 reference statements)

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“…The introduction of additives of lithium compounds is considered to be an effective way of regulating the expansion deformations of concrete due to the interaction between the aggregate and the alkaline medium of the cement stone [7,8]. Lithium compounds can be introduced both at the stage of cement production into the raw charge and during the preparation of the concrete mixture.…”

Section: Research Of Existing Solutions To the Problemmentioning

confidence: 99%

Development of alkaline concrete on the basis of active aggregates

Kovalchuk

Zozulynets

2021

TAPR

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The object of the research is the process of directed structure formation in the body of alkaline concrete, made using a reactive aggregate, in this case, basalt, and the process of deformation development in such concrete. The problem with using reactive aggregates is that they cause alkaline corrosion. It manifests itself in the form of cracks and layers of gel-like substances that form at the point of contact of the aggregate with the cement stone. During the research, methods of physical and chemical analysis were used (X-ray phase, differential thermal and thermogravimetric analyzes, electron microscopy, infrared spectroscopy, microprobe analysis). And also methods of mathematical planning of experiments have been used for the dependence of the physical and technical properties of cements and the directions of their structure formation. Also, the research has been carried out based on the analysis of world achievements in solving the problem of alkaline corrosion of concrete. The possibility of joint operation of the matrix of alkaline cements and active aggregates, represented by basalt, has been determined. The component composition of alkaline cement has been optimized and the need to increase the amount of the alkaline component in the system for the normal course of structure formation processes has been proved. The study of the influence of technical factors and conditions of hardening on the development of processes of structure formation of the investigated compositions has been carried out. The deformation properties of fine-grained concrete based on slag-alkaline cement and basalt aggregate have been investigated. It is shown that the expansion deformations of the samples, which accompany the process of alkaline corrosion of the aggregate in concrete, are directly related to the component composition and hardening conditions of the material. The obtained research results confirm the possibility of using active aggregates for the manufacture of building materials, in particular, based on alkaline cements. But for the safe course of the processes of structure formation, the component composition of the system has to be adjusted by introducing an active mineral additive and an additional alkaline component. The use of hydrophobizing additives makes it possible to increase the strength of the material even when operating under normal heat and humidity conditions.

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Section: Research Of Existing Solutions To the Problemmentioning

confidence: 99%

Development of alkaline concrete on the basis of active aggregates

Kovalchuk

Zozulynets

2021

TAPR

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“…It is generally believed that CH is one of the reasons for the poor strength of concrete. Research has shown that the high pozzolanic activity of MK − can consume CH and produce dense gel materials, which attracts researchers’ interest in the removal of the CH. , If high-activity MK replaces cement, it can quickly remove CH from the system and accelerate the hydration of OPC, thereby offsetting the strength loss caused by the dilution effect of mineral admixtures. In a word, understanding the reaction between MK and CH is the first step for revealing the reinforced mechanism of MK on concrete.…”

Section: Introductionmentioning

confidence: 99%

Molecular Insight into the Pozzolanic Reaction of Metakaolin and Calcium Hydroxide

et al. 2023

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The reaction mechanism of the pozzolanic reaction of metakaolin (MK) from the atomic point of view has not yet been explored. To explain the process and mechanism of the pozzolanic reaction from the atomic point of view, molecular insight into the pozzolanic reaction of MK and calcium hydroxide (CH) was analyzed through the reaction molecular dynamics (MD) simulation. The results show that the pozzolanic reaction of MK and CH can be essentially regarded as the CH decomposition and penetration into MK. Also, the structure evolution after the pozzolanic reaction shows that the water molecules cannot penetrate the MK structure till the participation of Ca2+ and OH– ions of CH. The Ca2+ and OH– ions have strong interaction with MK and drill into the MK structure, followed by the destruction of a part of the MK structure and water penetration. The final structure of CH removed by MK can be regarded as the precursor of the CASH gel structure.

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“…6 In recent years, the RAC has been widely studied. 7,8 However, RCA has defects, such as high porosity, high water absorption, micro-cracks, and complex sources, resulting in a slightly lower strength of RCA than natural coarse aggregate (NCA). Even so, researchers believe that the study of RCA is still of research significance.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on mechanical properties of recycled aggregate concrete with polypropylene fiber under combined compression‐shear loading

Liu,

Chen,

Shen

et al. 2023

Structural Concrete

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To investigate the mechanical properties of polypropylene fiber recycled aggregate concrete (PPFRAC) under compression‐shear, 69 recycled aggregate concrete (RAC) specimens were tested with the parameters of polypropylene (PP) fiber volume content (0, 0.6, 0.9, and 1.2 kg/m3), recycled coarse aggregate (RCA) replacement rate (0%, 30%, 50%, 70%, and 100%), and normal stress (0, 3, and 6 MPa). In the tests, the failure pattern of the specimens was observed, and the effects of the polypropylene fiber content on the direct shear stress, compression‐shear stress, initial shear stiffness, and shear ductility coefficient of the PPFRAC were thoroughly investigated. The results show that as the polypropylene fiber content increases, the direct shear stress of concrete (Natural aggregate concrete and 100% recycled coarse aggregate concrete [100%RCA]) first increases and then decreases gradually. Meanwhile, the best PP fiber content is 0.9 kg/m3 in this study. Furthermore, the compression‐shear stress‐displacement curves of specimens were obtained. The compression‐shear strength under normal stress at 6 MPa is approximately 230% greater than at 0 MPa. However, the peak shear stress of concrete is almost not affected by the replacement rate of RCA. Finally, based on the Mohr circle theory, the compression‐shear calculation model of PPFRAC is verified, and the optimal calculation formula is given.

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Alkali-aggregate reaction in recycled aggregate concrete

Cited by 63 publications

References 58 publications

Development of alkaline concrete on the basis of active aggregates

Development of alkaline concrete on the basis of active aggregates

Molecular Insight into the Pozzolanic Reaction of Metakaolin and Calcium Hydroxide

Experimental study on mechanical properties of recycled aggregate concrete with polypropylene fiber under combined compression‐shear loading

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