Building Construction Paper 1, May/June. 2011  
Questions: 1 2 3 4 5 Main
General Comments






























Question 2


(a)       State the difference between insitu and precast as used in concrete work.

(b)       Explain the reason for performing each of the following operations in concrete
            (i)        batching of constituent materials;
            (ii)       mixing of batched materials;
            (iii)      curing of placed concrete.

(c)       State the conventional mix ratio for each of the following:
            (i)        mass concrete;
            (ii)       reinforced concrete.

(d)       Name one mechanical plant suitable for each of the following operations:
            (i)        site clearance;
            (ii)       trench excavation;
            (iii)      pit excavation;
            (iii)      earth moving.

      Most candidates were able to state the :

     -          difference between insitu and precast concrete;
     -          conventional mix ratio for mass concrete.

     However,they failed to:

     -           explain the reason for performing the given operations during concrete production;

     -           name mechanical plant suitable for the given preliminary operations on site.

     The expected response to question 2 is as given below:

2 (a) (i)           Insitu concrete is placed wet in its permanent position while the pre-cast concrete
                        is produced elsewhere, allowed to harden and erected in the desired position.

    (b)(i)            The constituent materials in concrete are batched to ensure that they are accurately
                        measured by volume or weight according to the specified mix proportion.

        (ii)           It is done to ensure that the constituent materials are properly blended to achieve a
                        uniform or homogenous mass.
        (iii)          Placed concrete is cured to ensure that sufficient moisture is available for hydration
                       of the cement to achieve maximum strength.

      (c)(i)         mass concrete – 1: 3: 6

           (ii)        reinforced concrete – 1: 2: 4 OR 1: 11/2: 3

      (d)(i)        site clearance – bulldozer, grader.

          (ii)        trench excavation – Trencher, backacter;

          (iii)      pit excavation – Dragline with a grab.

          (iv)     earth moving – scraper, bulldozer, pay loader


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