Development of Draft Protocol for Testing of Structural Components and Systems

(a joint initiative of MoHUPA under technology submission of Pradhan Mantri Awas Yojna & IIT, KANPUR)

Concrete Masonry - Blocks

Concrete blocks are made from cast concrete, e.g. Portland cement and aggregate, usually sand and fine gravel for high-density blocks. Lower density blocks may use industrial wastes as an aggregate. It has many advantages, such as durability, strength and structural stability, fire resistance, insulation, sound absorption and economical construction. Concrete masonry units are used for both load-bearing and non-load bearing walls, partitions and panel walls. Concrete masonry building units which are used in the construction of load-bearing and partition walls such as Hollow and Solid load-bearing and non-load bearing concrete blocks shall conform to the IS: 2185-1 (2005) as given below.

Dimension and Tolerance: The nominal dimensions of concrete block shall be as follows-

  1. Length: 400, 500 or 600 mm.
  2. Height: 200 or 100 mm
  3. Width: 50, 75, 100, 150, 200, 250 or 300 mm

Full length and half-length U-blocks may also be manufactured for the purposes of band and lintels. The variation in the length of the units shall not be more than ±5 mm and variation in height and width of units, not more than ± 3 mm. The thickness of the face shell and web shall be not less than the values given in Table 1.

Table 1: Minimum face shell and Web Thickness as per IS: 2185-1 (2005)



Classification: The hollow (open and closed cavity) concrete blocks shall conform to the following two grades-
  1. Grade A: These are used as load bearing units and shall have a minimum block density of 1500 kg/m3. These shall be manufactured for minimum average compressive strengths of 3.5, 4.5, 5.5, 7.0, 8.5, 10.0, 12.5 and 15.0 N/mm2 respectively at 28 days
  2. Grade B: These are also used as load bearing units and shall have a block density between 1100 kg/m3 and 1500 kg/m3. These shall be manufactured for minimum average compressive strengths of 3.5 and 5.0 N/mm2 respectively at 28 days Solid Concrete block is classified as grade C-
  3. Grade C: The solid concrete blocks are used as load bearing units and shall have a block density not less than 1800 kg/m3. These shall be manufactured for minimum average compressive strength of 4.0 and 5.0 N/mm2 respectively

Materials: following materials are to be used in the construction of concrete blocks-
  1. Cement: Cement complying with any of the Indian Standards mentioned in clause 6.1 of IS: 2185-1 (2005) may be used
  2. Aggregate: The aggregates used in the manufacture of blocks at the mixer or the mixing platform shall be clean and free from deleterious matter and shall conform to the requirements of IS 383
  3. Fly ash: Fly ash conforming to IS 3812 (Part 2) may be used for part replacement of fine aggregate up to a limit of 20 percent
  4. Water: Water shall conform to the requirements of IS 456 and shall be free from material harmful for concrete such as matter likely to cause efflorescence
  5. Additives or Admixtures: They may be accelerating, water reducing, air-entraining and super plasticizer conforming to IS 9103 or may be Waterproofing agents conforming to IS 2645, and Coloring pigments.
Physical Requirements: The important physical properties of concrete blocks are as follows-
  1. Dimension: The overall dimensions of the units when measured as given in IS: 2185-1 (2005) Annex B shall in accordance with requirements as stated earlier in 1
  2. Block Density: The block density when determined as in IS: 2185-1 (2005) Annex C shall conform to the requirement given in Table 2.
  3. Compressive strength: When tested in the manner described in IS: 2185-1 (2005) Annex D shall be as prescribed in Table 2.
  4. Water absorption: The water absorption, being the average of three units, when determined in the manner prescribed in IS: 2185-1 (2005) Annex E shall not be more than 10 percent by mass.
  5. Drying shrinkage: Shall be determined in the manner described in IS: 2185-1 (2005) Annex F and shall not exceed 0.06 percent
  6. Moisture Movement: The moisture movement of the dried blocks on immersion in water, being the average of three units, when determined in the manner described in IS: 2185-1 (2005) Annex G, shall not exceed 0.09 percent.

    Tests: Tests as described in IS: 2185-1 (2005) Annex B to Annex G shall be conducted on the samples of units selected to ensure conformity with the physical requirements.

    Table 2: Physical Requirements as per IS: 2185-1 (2005)



    IS: 1905 recommend to determine compressive strength of masonry by prism test (fig. 1) as given below.
    1. Masonry prisms should be at least 40 cm high and shall have a height to thickness ratio (h/t) of at least 2 and not more than 5.
    2. Prisms shall be tested after 28 days between sheets of plywood by applying uniformly distributed load at a rate of 350 to 700 kN/m.
    3. If h/t ratio is less than 5 and greater than 2, correction should be as per Table 3
    4. IS 1905 also recommends to calculate the permissible compressive stress based on compressive strength of brick by applying suitable reduction factors as per Table

    Figure 1: Masonry prism tes



    Courtesy: Dr. Vaibhav Singhal and Mr. Syed Humayun Basha

    Table 3: Correction factors for different h/t ratio as per IS 1905



    Table 4: Basic compressive stresses for Masonry as per IS 1905



    ASTM C-1197: Recommended in Situ Measurement of Masonry Deformability Properties Using the Flatjack Method
    1. This test describes an in situ method for determining the deformation properties of existing unreinforced solid-unit masonry. This test method concerns the measurement of in-situ masonry deformability properties in existing masonry by use of thin, bladder-like flatjack devices that are installed in cut mortar joints in the masonry wall. This test method provides a relatively nondestructive means of determining masonry properties.
    2. Two flatjacks inserted into parallel slots, one above the other, in a solid-unit masonry wall are pressurized, thus inducing compressive stress on the masonry between them. The installation is shown in Fig. 2. By gradually increasing the flatjack pressure and measuring the deformation of the masonry between the flatjacks, load-deformation (stress-strain) properties may be obtained. Maximum compressive strengths may also be measured in certain cases. For further details of flatjack test method, please refer to ASTM C-1197 [1].

    Figure 2: Flat jack Testing Equipment



    Source: www.masonrysociety.org

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