Concrete Life Research Articles

Study of self-healing properties in concrete with bacteria encapsulated in expanded clay

Preparation process and life service solicitations can cause damage on concrete's internal structure, creating cracks that tend to propagate and increase with time. This poses a risk of failure as water penetrates, corroding the rebar reducing concrete's life span. Cement can exhibit up to a certain extent a natural ability to self-heal, consequence of the long-term hydration phenomenon. Some initial cracks can be spontaneously closed if the right conditions are met (humidity). However, it will not be enough to repair major cracks formed internally over a long period of use, so strategies need to be developed to achieve an efficient level of self-healing. This need lead to a new concept – self-healing. The biological approach is a suitable alternative to achieve healing in concrete. In this work, bacteria were immobilised in expanded clay and added to concrete by aggregate replacement.

Freeze/Thaw Performance of Concrete Using Granulated Rubber Crumb

This paper evaluates the properties and use of recycled rubber tyres in the form of rubber crumb as a freeze/thaw protection agent when used in concrete. Reusing scrap tyres in the form of rubber crumb in concrete could benefit the environment by contributing to the percentage of tyres used for a variety of recycling processes such as carpet underlay or tyre derived fuel, thus reducing disposal of tyres to landfill sites and the chemical usage of air entraining agents as a means of achieving freeze/thaw protection.Concrete cubes of 100mm were produced from design mixes which have been classified as plain, air entrained and rubber crumb and subjected to freeze/thaw cycles at 5 days of age.Thawing was conducted in water to ensure full saturation of pores and maximum stress on the concrete samples. The rubber crumb and plain concrete mixes were compared against the freeze/thaw performance of that entrained with air. Air entrainment is known to protect against freeze/thaw action.Rubber crumb when used at a 0.5% addition by volume provided the optimum freeze/thaw protection whilst maintaining the maximum compressive strength. The research shows that rubber crumb was effective at providing freeze/ thaw protection albeit with a reduced compressive strength when compared to air entrained concrete. The practical constraints of the test program were time and freezer space so the test was limited to 50 freeze/thaw cycles, which was sufficient for conclusions to be drawn.This paper contributes to the understanding of the effects of varying doses of rubber crumb in concrete when used as a freeze/thaw protection additive. The final compressive strength of the concrete mixes tested at freeze/thaw and non freeze/ thaw conditions are determined. The compaction of concrete is raised as an area of concern with regard to rubber particle separation within the plastic phase of the concrete's life.