Addressing the need for standardization of test methods for self-healing concrete: an inter-laboratory study on concrete with macrocapsules

Abstract

Development and commercialization of self-healing concrete is hampered due to a lack of standardized test methods. Six inter-laboratory testing programs are being executed by the EU COST action SARCOS, each focusing on test methods for a specific self-healing technique. This paper reports on the comparison of tests for mortar and concrete specimens with polyurethane encapsulated in glass macrocapsules. First, the pre-cracking method was analysed: mortar specimens were cracked in a three-point bending test followed by an active crack width control technique to restrain the crack width up to a predefined value, while the concrete specimens were cracked in a three-point bending setup with a displacement-controlled loading system. Microscopic measurements showed that with the application of the active control technique almost all crack widths were within a narrow predefined range. Conversely, for the concrete specimens the variation on the crack width was higher. After pre-cracking, the self-healing effect was characterized via durability tests: the mortar specimens were tested in a water permeability test and the spread of the healing agent on the crack surfaces was determined, while the concrete specimens were subjected to two capillary water absorption tests, executed with a different type of waterproofing applied on the zone around the crack. The quality of the waterproofing was found to be important, as different results were obtained in each absorption test. For the permeability test, 4 out of 6 labs obtained a comparable flow rate for the reference specimens, yet all 6 labs obtained comparable sealing efficiencies, highlighting the potential for further standardization.

Evaluation of Methodologies for Assessing Self-Healing Performance of Concrete with Mineral Expansive Agents: An Interlaboratory Study

“…However, the variation of the uncracked series of the lab, though surprising, can be explained by operator sensitivity and imperfect waterproofing. The former can be exacerbated by systematic errors and different environmental factors as previously reported by [ 10 ].…”

“…The surface penetration depth was not considered, only the ingress from the healed crack; thus, the ability for the healed section to hinder the ingress of chlorides could be evaluated. The application of the Trainable Weka Segmentation to analyse images within the context-enabling characterization of cementitious components shows great promise [ 10 , 36 , 37 ]. Once the images were manually checked, the area of chloride ingress around the crack was determined.…”

“…Previous work reported in literature has focused in paste or mortar [ 6 , 12 , 13 ], inadvertently neglecting to account for effects of dilution of healing agents on the self-healing efficiency as their addition is typically bound to cement fraction. To better reflect on the range of healing mechanisms developed in the literature and allow for a more comprehensive assessment, within the remit of the SARCOS Action, each of the six round robin tests focused on a different self-healing technique: (1) concrete with mineral additions, (2) concrete with the addition of magnesium oxide, (3) concrete enhanced with crystalline admixtures, (4) high-performance fibre-reinforced concrete enhanced with crystalline admixtures, (5) concrete with preplaced macrocapsules containing polymeric healing agent [ 10 ], and (6) concrete with encapsulated bacteria.…”

Self-healing concrete-What Is it Good For?

“…Six interlaboratory testing programs are being developed in the framework of the COST Action SARCOS. One program has already been finished (135), and the six laboratories involved obtained comparable sealing efficiencies, highlighting the potential of the methods used for further standardisation. However, further research is needed to obtain standard methods as well as accurate theoretical models, and, in a later stage, to evaluate the improved expected life span.…”

Polymer Flexible Joint as a Repair Method of Concrete Elements: Flexural Testing and Numerical Analysis

“…Cracked concrete is unable to transfer tensile forces thus various repair and strengthening methods of it are used [ 4 ]. Filling of cracks by external injection with bonding material such as epoxy resin or self-healing methods [ 5 , 6 ] use mainly stiff and high strength, but hardly deformable materials, which generate stress concentrations in concrete weakened by micro-cracks [ 4 ]. Recovering of strength and stiffness in damaged cross-sections leads also to the use of composite materials [ 7 , 8 ] with various adhesives [ 9 , 10 ].…”