Sealing of cracks in cement using microencapsulated sodium silicate

Abstract

Cement-based materials possess an inherent autogenous self-healing capability allowing them to seal, and potentially heal, microcracks. This can be improved through the addition of microencapsulated healing agents for autonomic self-healing. The fundamental principle of this self-healing mechanism is that when cracks propagate in the cementitious matrix, they rupture the dispersed capsules and their content (cargo material) is released into the crack volume. Various healing agents have been explored in the literature for their efficacy to recover mechanical and durability properties in cementitious materials. In these materials, the healing agents are most commonly encapsulated in macrocontainers (e.g. glass tubes or capsules) and placed into the material. In this work, microencapsulated sodium silicate in both liquid and solid form was added to cement specimens. Sodium silicate reacts with the calcium hydroxide in hydrated cement paste to form calcium-silicate-hydrate gel that fills cracks. The effect of microcapsule addition on rheological and mechanical properties of cement is reported. It is observed that the microcapsule addition inhibits compressive strength development in cement and this is observed through a plateau in strength between 28 and 56 days. The improvement in crack-sealing for microcapsule-containing specimens is quantified through sorptivity measurements over a 28 day healing period. After just seven days, the addition of 4% microcapsules resulted in a reduction in sorptivity of up to 45% when compared to specimens without any microcapsule addition. A qualitative description of the reaction between the cargo material and the cementitious matrix is also provided using x-ray diffraction analysis.

Enhancement of Recycled Aggregate Concrete Properties by a New Treatment Method

“…Sodium silicate will consume the amount of portlandite (CH crystal) in RCA to form C-S-H gel according to reaction (1). As a result, the properties of RCA have been enhanced such as decreased permeability and increased hardness [12]. Na2SiO3+H2O+Ca(OH)2→ x(CaO.SiO2)H2O+Na2O (1) Furthermore, pozzolanic powders contain a high content of Silicon (Si) and Aluminun (Al) which reacts with an alkaline solution and sodium silicate to generate a gel [13].…”

Validation of Self‐Healing Properties of Construction Materials through Nondestructive and Minimal Invasive Testing

“…In cementitious materials, many healing agents can be used. Microscopic analysis has been applied to study microcapsules containing different healing agents, expansive agents and crystalline products, synthetic microfibers, steel fibers, superabsorbent polymers, bacterial spores, among others. Microscopic analysis is used to determine the size and the morphology of the healing agents.…”

“…By looking at a structure with the naked eye, conclusions can be drawn on the distribution. Furthermore, the distribution of microcapsules at a surface can be studied by means of microscopy, and the macropores formed by SAPs can be studied as well . The found capsules and macropores should evenly be distributed.…”

An Experimental Study of Self Healing of Cracks in Concrete Using Sodium Silicate Capsule

“…The healing process of crack in concrete sample is observed by using ultrasonic non-destructive concrete tester (UX4600). The reaction which takes place in the healing mechanism is between calcium hydroxide present in the concrete and the sodium silicate to form crystal like substance which arrests the cracks 11 . Such recovery can occur independently 12 .…”