Preparation And Characterization Of Chloride Ion Or Carbonate Ion Triggered Microcapsules For Self-healing Concrete Application

Concrete is the construction material most widely used with the largest amount in the word. The most concerned problem about this material is deterioration, which involves buildings’ durability and lifetime. Deterioration is mainly caused by the corrosion of rebar embedded in concrete, and the corrosion are aroused by the permeation of chloridions and carbonate ions. So chloride damage and carbonation are the major problem for a civil engineering. To solve this issue, Cl--sensitive and CO32--sensitive microcapsules containing corrosion inhibitor are designed and prepared respectively in this thesis. It’s believed, embedment with these microcapsules will endue concrete with anti-corrosion ability, hence improve the construction’s service life and reliability.This paper employs sodium monofluorophosphate(Na2PO3F) as the rusty retardant agent of rebar. It was microencapsulated with polyacrylic silver( PAA-Ag) or the mixed complex of silver and copper, PAA-(Ag/Cu), by spray drying-salt solution bath method to form a Cl--triggered microcapsule, and with lead stearate by phase separation method to form a CO32--triggered microcapsule. The formation mechanism of microcapsules’ shell were discussed in details. The ion-trigger principle and prerequisites of shell were analyzed. After microencapsulation, the morphologies and mechanical properties of microcapsules obtained are studied.The results show, both of the two microcapsules are walled by a smooth, tight and strong enough shell, It will be profitable to protect the core of Na2PO3 F from being dissolved into water. In 3.5wt% Na Cl solution, PAA-Ag shell responds Cl- very quickly, can disperse in 3min. After doped with Cu2+, the strength are improved, but response time is extended. When mole ratio of Ag+/Cu2+ is 2:1, the response time of PAA-(Ag/Cu) is prolonged to 5min. However, once the mole ratio of Ag+/Cu2+ is less than 2:1, the shell only be swelled, doesn’t collapse. Instrumental analyses reveal, the response of Na2PO3F/PAA-(Ag/Cu) microcapsule to Cl- is caused by the Ag Cl precipitation reaction between PAA-Ag and Cl-. This reaction doesn’t happened between PAA-Cu and Cl-. In 3.5wt% Na2CO3 solution, the response time of Na2PO3F/lead stearate microcapsule to CO32- is 6hrs.When there exists OH- ion in water, PAA-Ag and lead stearate shells are not stable. They are inclined to react with OH- by forming Ag OH and Pb(OH)2 sediment respectively, so can’t respond to Cl- and CO32- ions any more.