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Acceptance Tests on Fiber Cement Flat Sheets– Part-2 of 2

Acceptance Tests on Fiber Cement Flat Sheets- Part 2 of 2

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Fiber cement flat sheets are made of an inorganic hydraulic binder or a calcium silicate binder fanned by the chemical reaction of a calcareous and siliceous material reinforced by organic fibers and inorganic synthetic fibers.

Fiber cement flat sheets

An acceptance test aims to establish whether a batch of products conforms to a given specification. The tests shall be carried out on samples drawn either from continuous production or from a delivered consignment.

Sampling of Test Specimen

In a consignment, all the sheets of identical size, category, and type, with even thickness and manufactured under similar conditions shall be grouped to constitute a lot. The number of sheets to be selected from the lot shall be as per the table given below:

Size of the LotSample Size
≤ 1503
151 to 1803
181 to 5004
501 to 12005
1201 to 32007
3201 to 1000010
Table 1: Sampling of test specimen

Test on Fiber Cement Flat Sheets

4. Warm Water Test

This test determines the possible degradation of products by keeping them in warm water for a protracted period.

Specimen Preparation

  1. 10 sets of paired specimens are cut to suit the bending test specimens.
  2. Each specimen pair shall be cut adjacent from a single sheet, and the same number is given for later comparison of results.
  3. The apparatus shall include the following items:

a. Water bath capable of temperature control to 60 ± 5°C
b. Testing equipment for determination of bending strength as described above.

Test Procedure

  1. 10 specimens of the second lot are immersed in water at 60 ± 5°C saturated with a product of the same composition for 56 ± 2 days.
  2. At the end of this period, the specimens are placed in a laboratory atmosphere for 7 days.
  3. After preliminary conditioning, the wet bending test shall be carried out as given in Part-1.

Result Interpretation

For each pair of the specimen, i (i =1 to 10), the individual ratio r1 is calculated as follows:

Where,

Rf1 is the modulus of rupture of the ith test specimen after 50 freeze-thaw cycles.

Rfc1 is the modulus of rupture of the ith reference test specimen.

The standard deviation, S, and average, r, of the individual ratios r1 are calculated.

Calculate the 95% lower confidence limit, L1 of the average ratio, as follows:

L1=r-0.58s 

The limit L shall be greater than 0.75

5. Soak Dry Test

Specimen Preparation

  1. 10 sets of paired specimens are cut to suit the bending test specimens.
  2. Each specimen pair shall be cut adjacent from a single sheet, and the same number is given for later comparison of results.
  3. The test apparatus shall include the following:
    1. Ventilated oven capable of achieving a temperature of 60 ± 5°C and relative humidity of less than or equal to 20% with a full load of specimens.
    2. Bath filled with water at ambient conditions.
    3. Apparatus for bending test as defined in bending test.

Test Procedure

  1. The specimens are divided into two lots of 10 specimens.
  2. After the conditioning procedure, the first lot of 10 specimens to the bending test is carried out as described in part 1. 
  3. At the same time, the second lot is submitted to 25 soak-dry cycles consisting of
    1. Immersion in water at ambient temperature for 18hrs,
    2. Drying in a ventilated oven of 60 ±5°C and relative humidity of less than 20% for 6h.
  4. If necessary, an interval of up to 72 h between cycles is allowed.
  5. During the interval, specimens must be stored in immersed conditions.
  6. After 25 cycles, the specimens are placed in a laboratory atmosphere for 7 days. At the end of this period, the wet bending test is carried out as specified.

Result Interpretation

For each pair of the specimen, i (i =1 to 10), the individual ratio r1 is calculated as follows:

Where,

Rf1 is the modulus of rupture of the ith test specimen after 50 freeze-thaw cycles.

Rfc1 is the modulus of rupture of the ith reference test specimen.

The standard deviation, S, and average, r, of the individual ratios r1 is calculated.

Calculate the 95% lower confidence limit, L1 of the average ratio, as follows:

L1=r-0.58s

The limit L shall be greater than 0.75.

6. Heat Rain Test

This test provides an optional test method to assess the performance of a cladding system composed of fiber cement sheets in a particular installation (sub­frame and fixings) under cyclic changes of moisture and heat. This test is carried out on finished products.

Principle

Sheets are fixed to a building frame according to the manufacturer's recommended installation practices. The sheets are then subjected to alternate wetting and heating cycles, following which any structural alteration is recorded.

Apparatus

  1. A sub-frame to which the sheets under test shall be fixed vertically.
  2. The water spray system provides complete wetting of one face.
  3. A heating system to provide uniform radiant heat to give blackbody temperature across a complete test frame surface of 60 ± 5°C and approximately uniform power output during the cycle.
  4. A control system allowing the test conditions to alternate automatically shall be installed as prescribed in the test procedure.

Test Procedure

  1. Select a representative installation system. Assemble the system according to the manufacturer's recommendations.
  2. The construction should include a provision for at least one sheet joint in its central region.
  3. The frame dimensions shall have a minimum area of 3.5 m2 and allow at least two sheets to be installed with normal orientation.
  4. Fix the sample sheets to the test frame observing all the manufacturer's recommendations.
  5. The edge fixing distance should be the minimum allowed, and the center distance between fixings should be the maximum allowed.
  6. The sheets shall include all weatherproofing and other attachments generally specified in the assembly.
  7. The assembled frame is subjected to the following test cycle:
    • Water spray: 2hrs 50 min
    • Pause: 10 min
    • Radiant heat: 2hrs 50 min
    • Pause: 10 min
  1. The sheet assembly shall be submitted to 25 cycles.

Result Interpretation

On completion of the final test cycle, an inspection of the sheets is carried out for damage or structural alteration caused by the test and to assess the product for visual defects against the requirement:

When tested, any visible cracks, delamination, or other defects in the sheets shall not be of a degree affecting their performance in use.

Read More:

Acceptance Tests on Fiber Cement Flat Sheets – Part-1 of 2

Fiber Cement Flat Sheets: Types, Characteristics, Tests, and Advantages

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