Tracking cracks in structures

Expansion and shrinkage due to temperature, humidity and loading happen to all construction materials, resulting in cracks.

18bgp-greensens_18_1723540eWhat discourages people from building with natural materials? Why are there very few buildings using them, despite people knowing much about the cost and performance advantages of mud, stone, bricks, wood, bamboo and clay? Eco-friendly architecture nurtured human settlements for thousands of years, yet our generation seems to be discarding the idea. Are there reasons for rejection other than material scarcity or vanishing skill?

Apprehensions of many kinds are among the major reasons and cracks are among the major apprehensions. All buildings crack, irrespective of them being sustainable or consuming; local or global. Expansion and shrinkage due to temperature, humidity and loading happen to all construction materials, resulting in cracks. Some could be invisible; the visible ones could be small or big; they may appear in wall or window; some may appear and disappear periodically. If so, cracks are not an inherent characteristic of sustainable buildings only built with natural materials or alternative technology. Yet, the pretext of cracks is often sighted to discourage people from constructing an eco-friendly building.

It is not easy to decipher cracks to be structurally dangerous or not. Mostly what we get to see is surface cracks in plastered walls, small angular lines in the corners of window bottoms, some narrow cracks in the edge of lintels, horizontal gaps where concrete beam touches brick wall or slab bottom, vertical cracks along concrete columns and such others, all of which are harmless. There are valid reasons such as shrinkage of material, differential wall weight around window openings, ignoring code of practice, speed of construction, lack of supervision, and non-compatibility of two materials like RCC and bricks when placed adjacent to each other. All these are commonly seen in conventional plastered buildings also.

Contrary to the common belief, in case of exposed materials, we tend to see less of cracks, with the joints absorbing and concealing them. If we try composite wall, i.e. with different materials for outside and inside, people worry that they may separate with a gap in between. This does not normally happen because of material bonding and mortar packing in between.

When wall materials like clay block or stabilised mud block end at a concrete column, they should not be touching it, but be segregated by a mortar joint, which will ensure no visible cracks.

Walls with natural materials, if very long or wide, may develop cracks following the shrinkage in volume. Hence, it is advisable to break the area by openings, lintels, concrete bands and such others to reduce the risk. Filler slabs, if laid across large spans, may develop cracks; hence need expansion joints, just like normal RCC roof. Arches and vaults tend to shrink, hence crack. All these cited cases normally do not fail structurally. Once we refinish it with crack fillers, they get covered up and the cracks will not reappear.

There are specific cracks that denote structural implications, which need to be studied in more detail, lest we may assume all cracks to be harmless.

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Posted on January 18, 2014, in concepts, fundamentals and tagged , . Bookmark the permalink. Leave a comment.

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