engineer

Please add No 29. Poorly prepared subgrade under slab.

Hello eriew

Appreciate your #29 addition to my above quick reply re causes of concrete slab failure.

from me

Kind Regards....

1. incorrect cement ratio to what? water:cement ratio? water:cement ration affects the strength and workability of concrete. the lesser the water the more strength on concrete but lower workability. we ussually apply additives to improve the workability of concrete.

2. slab loaded before curing completed - in practice, specially building construction, three days after concreting the slab, preparation for the construction of columns, beams & slabs on the next level will commence while curing is on-going. it is very impractical to wait to complete the curing period before you proceed to the next. this will cause delay on construction. to avoid any damage or cracks on newly poured concrete, additional supports will be installed on the soffit to decrease the span length of the structures specially on beams. take note that on any formula for computing the moment, moment load is directly proportional to the span length. the lesser the span, the lesser the moment load. may we say that insufficient temporary supports on the newly concrete slab will cause cracks.

3. too many fine aggregates - how about the plastering? it is a mixture of cement, sand and water. cracks oocured on plastering is due to thermal or wrong methodology of application. therefore, too many fine aggregates is invalid reason.

4. curing time too fast - another invalid reason. in practice, we ussually apply additives to speed-up the curing of concrete. sometimes we use different types of cement (type 3, 4 or 5, i forgot which type). rapid setting of concrete is one of the cause on cement cracks. clinker is already a cement, we add gypsum to slow down the setting of concrete not the beach sand. rounded aggregates is invalid reason. aggregates on river quarry is rounded. aggregates produced from crusher is angular.

what kind of slab you are reffering to? reinforced concrete or plain concrete? your question is very broad.

5. beach sand - using beach sand causes corrosion of steel, corrosion of steel causes the cracks on the slab.

Hello batchfil

You don't seem to have replied to the request for additional information.

Reply here, with

Kind Regards....

That fellow is right, you must be corrected or else we are feeding wrong informations. And one thing more, this is a discussion. You must accept their comments if your are wrong. They are speaking according to their knowledge and experiences. The only thing I can say to his/her comments, they are scrambled on the last part (from #4 to #5). As an engineer, I understand what he/she is saying. Please rearange your comments in order to understand for the non-technical people. Thank you.