36) The expansion of Portland cement is caused by

• (a) free lime
• (b) magnesia
• (c) silica
• (d) both (b) and (c)

37) The compressive strength of a good Portland cement and standard sand mortar after 3 days of curing should not be less than

• (a) 7 MN/m2
• (b) 11.5 MN/m2
• (c) 17.5 MN/m2
• (d) 21 MN/m2

38) The sand is mixed with lime mortar to

• (a) reduce cost
• (b) reduce setting time
• (c) improve strength
• (d) prevent shrinkage and cracking

39) Which of the following statement is correct ?

• (a) The sand used for making mortar should be fine.
• (b) The rounded grains of sand produce a strong mortar.
• (c) The mortar made with coarse sand is stronger than the one made with fine stand.
• (d) all of the above

40) For R.C.C. construction, the maximum size of coarse aggregate is limited to

• (a) 10 mm
• (b) 15 mm
• (c) 20 mm
• (d) 25 mm