1. Concrete masonry units are classified \"solid\" when the bearing surface or n

Question

1. Concrete masonry units are classified "solid" when the bearing surface or net cross sectional area is equal to or more than f the cross sectional area. a, 25%, b, 75%, c.7096, d.23, e. None ofthese 2. A wood construction unit was tested with the following results: Saturated mass of unit 317.5g Oven-dry mass of unit 203.9g Absorption ofmass unit 22% 3. Determine the moisture content of the wood construction unit. 4. Determine the moisture content as percentage of the wood construction unit. 5. Determine the free moisture content as a percent of total moisture. The strength of masonry construction is generally limited by one of the following. (Circle the correct answer.) 6. a. the mix of aggregates in the mortar b. the amount of cement in the mortar c. the ability to bond the units with mortar d. setting time of the mortar

Explanation / Answer

For question 1

ASTM defines CMU as solid if core area is not more than 25% of cross sectional area thus option B is correct .

In question 2 it has been given that :

Saturated mass of unit = 317.5 g

Oven dry mass of unit = 203.9 g

Thus water content = 317.5-203.9= 113.6 g

For question 3

Moisture content of saturated unit = ( weight of water/ weight of solids) * 100 = 113.6 * 100 / 203.9 = 55.7135 %

Moisture content at 22% absorption = 0.22* 203.9 = 44.858 g

For question 4 it is desired to determine moisture content as percentage of wood construction unit

Thus if we assume that wood construction unit is saturated , moisture content = 55.7135 %

For question 5

We have total absorption of 22% which equals 44.858 g of water

However saturated water content is 113.6 g

Thus free water = absorbed water = 44.858 g

Total moisture for saturated condition = 113.6 g

Hence free moisture content as percentage of total moisture content =( 44.858/ 113.6 )*100 = 39.48 %

For question 6 it is worth mentioning that the strength of masonry construction depends upon strength of bricks and mortar and also the thickness of brick mortar joint . The amount of cement determines the strength of mortar and hence it also limits the strength of masonry . Hence option B is correct.

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