Autogenous self-healing of cement with expansive minerals-II: Impact of age and the role of optimised expansive minerals in healing performance

Abstract

7This part of the study presents the optimisation of expansive minerals mix proportions and establishes 8 a quantitative and qualitative correlation between self-healing and the cracking age of cementitious 9 materials. The hydration degree of cementitious materials is considered as a quantitative measure of 10 age and the corresponding healing performance was analysed to establish an age-healing relation. 11Healing performances were assessed in terms of load recovery, crack sealing efficiency and gas 12 permeability. The microstructure of materials was investigated using XRD, TGA and SEM-EDX. The 13 self-healing performance of particular cement mixes shows linearly increasing correlation with the 14 reduction of hydration degree. However, cement mixes containing expansive mineral result in higher 15 healing performance than mixes containing only Portland cement (PC). This observation was 16 confirmed for all cracking ages. Blends containing only PC showed healing materials that were 17 mostly calcite and portlandite, while the optimised use of expansive minerals produced denser healing 18 materials with C-S-H, and complex Ca, Mg, Si, Al combined hydrated and carbonated products in 19 addition to calcite and portlandite. The results further suggest that the proportions of calcite, 20 portlandite and ettringite in healing compounds have an increasing trend with the age of hardened 21 cementitious materials. 22

Self-Healing Concrete and Cementitious Materials

“…Besides common healing compounds, calcite, portlandite, ettringite and C-S-H, MgO formed brucite, other magnesium hydro-carbonate products. Although, the healing capacity of cementitious materials decreases with the increase in the age of cement paste mix at crack formation, expansive minerals improved the autogenous selfhealing capacity of PC mixes at all ages compared to the 100% PC paste [18].…”

“…Cardiff University research group introduced polyethylene terephthalate (PET) tendons [7], a shrinkable polymer activated with a heating system inside the concrete structural element to compress and close the crack enhancing the autogenous healing process. Considerable enhancement in healing performance is also possible to achieve using optimum supplementary cementitious materials (SCMs) and smart expansive minerals [3,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Autonomic self-healing in concrete, in contrast to the autogenous healing Example of self-healing concrete and cementitious systems (Adopted from [3]).…”

“…Self-healing performance in concrete is assessed using visual observation, mechanical strength recovery, permeability, durability improvement and microstructural evaluation (Figure 3). There are three fundamental factors in evaluating the self-healing: visual crack sealing and the identification of healing compounds causing it, the improvement of the durability performance and the recovery of mechanical strength properties [3,[15][16][17][18][19][20][21]. The mechanical strength recovery is limited in most of the concrete self-healing process.…”

“…Magnesium oxide (MgO), bentonite clay and quicklime were used in different proportions to enhance the autogenous self-healing capacity of concrete and cementitious materials [3,[16][17][18][19][20][21]. Substitution of PC with up to 12.5-15% by a mix of the three expansive mineral agents, MgO 5-7.5%, bentonite clay 2.5-5%, and quicklime 2.5-5%, results in optimum enhancement of the autogenous self-healing in the cement mix [17,18]. A typical crack healing image is presented in Figure 8 that shows how efficiently the expansive mineral containing PC mix sealed 17o-μm crack in 28 days.…”

Biomimetic Self-Healing Cementitious Construction Materials for Smart Buildings

“…This deterioration is due to a range of both extrinsic and intrinsic processes related to the chemical, physical, thermal, and biological nature [ 2 , 23 ]. Furthermore, the impact of inadequate use and environmental conditions on how concrete performs has been highlighted in many studies [ 24 , 25 , 26 , 27 ]. Within construction industries, the prevention of the steel reinforcement exposure to hazardous chemicals such as corrosive agents depends significantly on the concrete.…”