Concrete Outline

Concrete is an artificial stone-like material used for various structural purpos-es. The word concrete originates from the Latin word concretus which literally means compact or condensed. Concrete has been used for many amazing things throughout history, including architecture, infrastructure and more. The Egyptians were using early forms of concrete over 5000 years ago to build pyramids. They mixed mud and straw to form bricks and used gypsum and lime to make mortars. Joseph Aspdin of England is credited with the invention of modern Portland ce-ment. He named his cement Portland, after a rock quarry that produced very strong stone.

Contrary to popular belief, concrete and cement are not the same thing; ce-ment is actually just a component

Portland cement mixed with sand, gravel and water, a process called hydration, is how concrete is created. Crushed stone aggregate fine and coarse aggregates make up the bulk of a concrete mixture. Durability of concrete may be defined as the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engi-neering properties. Different concretes require different degrees of durability de-pending on the exposure environment and properties desired. For example, concrete exposed to tidal seawater will have different requirements than an indoor concrete floor. Concrete does not require much water to achieve maximum strength. But a wide majority of concrete used in residential work has too much water added to the concrete on the job site. This water is added to make the concrete easier to install. This excess water also greatly reduces the strength of the concrete. Cracks in con-crete occur due to various mechanisms such as shrinkage, freeze-thaw reactions and mechanical compressive and tensile forces. Structural cracks in residential founda-tions usually result from settlement or horizontal loading. Most (but not all) struc-tural cracks resulting from applied loads are nearly horizontal (parallel to the floor) and occur 16” to 48” from the top of the wall. They are much more prevalent con-crete block construction. They can be brought about by hydrostatic pressure or heavy

Bio-concrete has been in the works since 2005, when Jonkers was first asked to come up with some kind of concrete that could effectively fix itself. He de-cided to try a new method of mixing concrete in which he’d add a “healing agent” in the form of bacillus bacteria that are capable of surviving in the harsh conditions inside concrete and remaining idle until activated. He then added calcium lactate to the concrete mixture to give the bacteria something to feed on that would make them produce the needed limestone as a waste bi-product. A consortium of 22 TU Delft research groups at Delft University of Technology are developing this tech-nology and trying to find more durable and sustainable materials and techniques that are currently running in parallel. The core purpose is to introduce self-healing mechanism particularly to constructions which are very liable to damage. To heal cracks in the concrete, Jonkers chose bacteria (Bacillus pseudofirmus and B. cohnii), that are able to produce limestone on a biological basis. The positive side-effect of this property: the bacteria consume oxygen, which in turn prevents the internal cor-rosion of reinforced concrete. However, the bacteria do not pose a risk to human health, since they can only survive under the alkaline conditions inside the concrete. Based on these findings, Jonkers and his team of researchers developed three differ-ent