Repeated autogenous healing in strain-hardening cementitious composites by using superabsorbent polymers

info:eu-repo/semantics/publishe

Effect of sample age on the self-healing properties of cementitious mateials with superabsorbent polymers

To obtain sustainable construction materials, occurring cracks in concrete should be repaired. However, as this often manual repair is time-consuming and expensive, self-healing may provide a solution. Autogenous healing is an already-present feature in cementitious materials, but it is an inferior mechanism as it can only heal cracks up to 30 μm in the presence of water. Therefore, a cementitious material with synthetic microfibres and superabsorbent polymers (SAPs) is proposed. Synthetic microfibres cause multiple crack formation with small healable cracks. Furthermore, SAPs are able to extract moisture from the environment and to provide it to the cementitious matrix for autogenous healing. But, if the building blocks are exhausted in time due to ongoing hydration, healing may be less efficient. In this study, the ability of (promoted) autogenous healing in time (7 days, 28 days, 3 months and 1 year) is investigated by comparing the mechanical properties after performing four-point-bending tests in different mixtures. The specimens were first loaded to 1% strain, stored in wet/dry cycles for 28 days and were subsequently reloaded. The results show that, with increasing age, the crack width decreases and a higher water-to-binder ratio tends to increase the mean and maximum crack width. All specimens are able to heal and to regain some of the mechanical properties after being preloaded and pre-cracked under four-point-bending. If SAPs are added, there is even healing in an environment without liquid water (relative humidity of more than 90%). At early age, the healing is governed by further hydration and calcium carbonate crystallization. At later ages (after one month), the main autogenous healing mechanism is the formation of calcium carbonate crystals. The amount of white precipitated healing products was higher in specimens with a higher water-to-cement ratio. Cracks in the specimens with fly ash were better closed in comparison with the samples with pure cement and blast-furnace-slag-blended mortars. Mixtures with SAPs showed more healing. The cementitious composite with microfibres and SAPs thus shows good self-healing in time

Barbex Plantations Ltd (Ghana). First technical assistance for coffee culture, 27 March to 10 April 1998

Cette première mission technique devait faire le point sur la plantation et son entretien, sur la préparation du terrain et les caractéristiques du sol, la fertilisation, les pépinières, la taille, la lutte antiravageur et le contrôle des maladies, l'organisation du travail et le traitement après récolte afin de proposer des solutions pour améliorer les pratiques actuelles, le rendement et la gestio