Effect of Carbonation Curing on Physical and Durability Properties of Cementitious Materials Containing AOD Slag

In this study, the physical and durability properties of cementitious materials containing stainless steel argon-oxygen decarburization (AOD) slag were investigated by CO2 curing. Three contents (0, 30, 60%) of ordinary Portland cement (OPC) were replaced with AOD slag. Specimens were cured at four CO2 concentrations and three temperatures. The chloride diffusion coefficient, drying shrinkage, compressive strength, and porosity were measured. The drying shrinkage reduction was proportional to CO2 uptake. The chloride diffusion coefficient increased as contents of the AOD slag increased. At 15% CO2 concentration, the diffusion coefficient was similar to that of the OPC regardless of the AOD slag substitution rate. The durability of cementitious materials mixed with AOD slag can be improved by CO2 curing and can be used in construction

Evaluation of Autogenous Healing in Flexural Mortar Members by Chloride Ion Penetration Resistance

In this study, we investigated the effects of mineral admixtures on the autogenous healing of flexural mortar members through a chloride ion penetration test. The mineral admixtures used were ground granulated blast-furnace slag (GGBS), fly ash, silica fume (SF), clinker binder, and clinker sand. Through a four-point bending test, a crack of approximately 100 μm was induced at the bottom of the flexural mortar member, and the chloride ion penetration depth through the crack was measured to evaluate the self-healing performance. Additionally, we analyzed the correlation between the self-healing performances, which was measured through water flow and water absorption tests. The experimental results showed that the chloride ion penetration depth decreased due to crack healing, and the self-healing performance of the GGBS and SF was the highest. It was found that the subtle change in the self-healing performance was more accurately evaluated by the chloride ion penetration test

Self-Healing Products of Cement Pastes with Supplementary Cementitious Materials, Calcium Sulfoaluminate and Crystalline Admixtures

The phase composition of self-healing products generated in cracks affects self-healing performance. This study investigated the self-healing products of cementitious materials using supplementary cementitious materials (SCMs), a calcium sulfoaluminate (CSA) expansion agent, and crystalline additives (CAs). Ground-granulated blast-furnace slag (GGBFS), fly ash (FA), and silica fume (SF) were used as SCMs, and anhydrite, Na2SO4, Na2CO3, and MgCO3 were used as crystalline additives (CAs). An artificial crack method was used to collect the self-healing products in the crack of the paste. The phase composition of the self-healing products was analyzed through X-ray diffraction (XRD)/Rietveld refinements and thermogravimetry/differential thermogravimetry (TG/DTG) analysis, and their morphology and ion concentration were examined through scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS). From the results, the main compound of self-healing products was found to be calcite. GGBFS and FA decreased the content of portlandite, and the use of CAs led to the formation of alkali sulfate and alkali carbonate. The SEM–EDS analysis results showed that when GGBFS and FA were used, a large proportion of the self-healing products contained C-S-H and C-A-H, and the use of CSA led to the formation of monosulfate and ettringite

Long-term autogenous healing and re-healing performance in concrete: Evaluation using air-coupled surface-wave method

This study aimed at investigating two original topics on self-healing concrete, 1) the prediction of long-term healing progress and 2) the evaluation of re-healing performance for a previously healed but reopened crack, using the air-coupled surface-wave method. Small-scale plate concrete specimens were fabricated with a selfhealing binder incorporating ground granulated blast furnace slag, Na2SO4, anhydrite, and graded clinkers. A single flexural crack of 0.25-0.30 mm width was generated near the mid-span of each specimen. Then, the specimens were kept immersed in water, and the healing progress of the cracks was monitored for approximately one year. As a result, the residual surface crack area was reduced to 15.1% of the fully-cracked condition, and the surface wave transmission ratio recovered up to 82.9% of the uncracked condition. A prediction model for the ultimate healing rate and initial healing rate was proposed based on surface-wave results. After the first selfhealing process, the specimens were loaded again, and a similar crack was produced at the previously healed zone in each specimen. Then, the re-healing performance was evaluated for about two months. From the second self-healing process, one specimen with a narrow reopened crack showed a satisfactory recovery in surface wave transmission, comparable to that in the first healing

Effect of Clinker Binder and Aggregates on Autogenous Healing in Post-Crack Flexural Behavior of Concrete Members

Crack healing has been studied extensively to protect reinforced concrete structures from the ingress of harmful ions. Research examining the regain in the mechanical properties of self-healing composites has focused mostly on the computation of the healing ratio based on the measurement of the tensile and compressive strengths but with poor regard for the flexural performance. However, the regain in the flexural performance should also be investigated for design purposes. The present study performs flexural testing on reinforced concrete members using crushed clinker binder and aggregates as well as crystalline admixtures as healing agents. Healing ratios of 100% for crack widths smaller than 200 μm and 85% to 90% for crack widths of 250 μm were observed according to the admixing of clinker binder and aggregates. Water flow test showed that the members replacing binder by 100% of clinker achieved the best crack healing performance. The crack healing property of concrete improved to some extent the rebar yield load, the members’ ultimate load and energy absorption capacity and ductility index. The crack distribution density from the observed crack patterns confirmed the crack healing effect provided by clinker powder. The fine grain size of clinker made it possible to replace fine aggregates and longer healing time increased the crack healing effect