hey guys, u may ask me anything about construction industry and i'll try my best to answer all ur question.

So the site engineer need to do slump test.

wrong bro, slump test to test the mobility of concrete la

concrete is just 1 type. depend what the strength of concrete u want. eg. if u order grade 40N concrete, mean that concrete can stand the force not below 40N/mm2. like he said need send to lab for cube test. however 21 days only u will know the final result as concrete need 21days to achieve that result which is 40N/mm2. usually after u cast a level, consulting engineer not allow u to cast another floor because they want o see the result first. but then also they don't want to hinder the process of work therefore they get the 7 days result. 7th day if got achieve desired strength maybe around 30N then they allow to proceed casting of next floor.

among so many readymix concrete supplier, YTL subsidiary aka buildcon concrete sdn bhd is the smartest concrete supplier. why I said so? the concrete they supply can achieve very close to 40N for 21 days strength maybe like 40.5N or 41N while the rest of concrete supplier achieve more maybe like 44N or 45N. yeah u not heard it wrong, why I said smart that YTL achieve close to 40N which less than other? it's because in concrete, the expensive ingredient is cement. the more cement, the higher the strength. YTL just so precise enough to control the quantity of cement they use so they won't use more but at the same time still can achieve the desire strength. the other supplier will use more because they afraid that the concrete strength will fall below hence they rather spend more cement and subsequently they can't achieve the best optimum qty like YTL do.

to answer ur 2nd question, it is due to the waterproofing layer damaged. it could be many reason, poor workmanship, when owner doing renovation punch through the layer. anyway, only kitchen, toilet and balcony require waterproofing layer on floor.

usually waterproofing vendor will give like 20 years warranty 1.

depend what u want as I said. example floor slab usually require grade 25N concrete. of course u can use grade 40N but for what wasting that money to get more strength than what it require? wall and column require grade 40N concrete. anyway the strength of concrete doesn't support ur house. the 1 which give the strength to support the entire building is the steel bar inside the concrete. concrete just give a little compressive strength and protect the steel from rusty.

waterproofing which 1 better? of course is membrane type la. abt RM90/m2