Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration

Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration

[ASTM C 1202: 2012]

·         Specimen: (100mm ø Casting Cylinder) or (cores from 150mm cubes and slabs) or (Cores from Site Structures)

·         Test Age: 28 or 56 days

·         Curing: Keep in water tank at (23 ± 2) °C and then remove from tank 2 days before testing.

·         Preparation of solutions:

3% NaCl = 970mL distilled water + 30g NaCl

0.3N NaOH = 1L distilled water + 12g NaOH Pellets

·         Preparation of specimen:

-          Extract core of 100mm ø from casting face of specimen

-          Trim the casting face (Top Surface) up to 5mm & cut slice of (50±3) mm thickness

-          Apply rapid setting coating (as insulator) to side surfaces of specimen and leave for dry 1day

·         Conditioning:

-          Place the specimen into vacuum desiccator and start vacuum pump.

-          Set pressure to be less than 50 mm Hg and maintain for 3 h.

-          Fill the vacuum desiccator by de-aerated water without stopping the vacuum pump and maintain for 1 h

-          Stop the vacuum pump and allow the air to re-enter the desiccator

-          Soak the specimen for (18±2)h and then remove from water for testing

·         Testing:

1.       Fix the specimen in the cell & Fill the side of the top surface with 3.0% NaCl solution which will be connected to the negative terminal of power supply. Fill the other side which will be connected to the positive terminal of the power supply with 0.3N NaOH solution

2.       Turn on the power supply and set to (60±0.1)V

3.       Record the initial reading of Current (mA) and Temperature (°C) (from NaOH Solution Side)

4.       During the test, the air temperature should be maintained in the range 20 to 25 °C

5.       Read and record current and temperature every 30 minutes until 6h (13 readings)

6.       Terminate the test if the temperature of solution exceeds 90°C before 6h

·           Calculation:

-          Total (mA) = I₀ +2(I₃₀ + I₆₀+ I₉₀+ I₁₂₀+ I₁₅₀+ I₁₈₀+ I₂₁₀+ I₂₄₀+ I₂₇₀+ I₃₀₀+ I₃₃₀) + I₃₆₀

-          Charge Passed (coulombs): Qx = (Total/1000)*900

-          Corrected Charge Passed (coulombs): Qs = Qx*(95/Ø)²

-          Indicate the Chloride Ion Penetrability based on the Charge Passed values as in table:

Charge Passed (coulombs)	Chloride Ion Penetrability
> 4000	High
2000 – 4000	Moderate
1000 – 2000	Low
< 1000	Very Low
< 100	Negligible

                                                                    

Compressive Strength of Concrete Cores

Compressive Strength of Concrete Cores

[BS 1881 – Part 120: 1983]

·         Specimens: 100 or 150 mm Dia, (Dia/Agg. Size ≥ 3), (Length/Diameter [λ] = 1 – 2).

·         Identification: Check Location, Orientation, Direction of Drilling relative to Direction of Casting and Min/Max Length as received.

·         Examination: Check the Excess Voids (%) by Comparing the Core Surface with Figure 1:

o   Small Void (0.5 – 3.0) mm.

o   Medium Void (3.0 – 6.0) mm.

o   Large Void (>6.0) mm.

o   Honeycombing (Interconnected Voids).

·         Dimension: to nearest 1mm (measure length and diameter before and after preparation)

·         Density (As Received, Moist, Saturated): to nearest 10 Kg/m³

·         Reinforcement: Measure the Size, Spacing of bars and Position in core (Center of bar to top of Core) as received and after preparation.

·         Tolerances: Flatness: 0.06 mm, Squarness: 2.0 mm wide, Parallelism: 2.0 mm wide & Cylindricity: 3 % of core diameter

·         End Preparation:

1.       By grinding: Store in Water (20 ± 2) °C, take out for 1h for grinding and measurement.

2.       By capping (<10mm Thickness):

a)      Store in Water (20 ± 2) °C, take out for 1h for Capping and measurement.

b)      Store in dry condition; take out for 1h for Capping and measurement.

·         Testing: Not less than 2 days after preparation and immersing in water

·         Loading: Pace Rate (0.2 -0.4)N/(mm².s)

·         Compressive Strength: to nearest 0.5 N/mm² (Load/Area)

·         Estimated In-Situ Cube Strength:

1.       Free of reinforcement: I.S.C.S =  x C.S (D = 2.5 horizontally drilled, 2.3 Vertically)

2.       Presence of reinforcement (Single Bar): Correction Factor = 1.0 + 1.5 (ø_r*d/ø_c*l)

3.       Presence of reinforcement (Two Bars): Correction Factor = 1.0 + 1.5 (Ʃø_r*d/f_c*l)

ø_r is diameter of Reinforcement

ø_c is diameter of Specimen

d is distance of bar from nearer end

l is length

Elongation index of the aggregate

Elongation Index of Aggregate

[BS 812 – Part 105.2: 1990]

·         Preparation of Specimens:

1.       Take quantity material of aggregate (bulk sample) randomly from source.

2.       Reduce the Sample to test portions by Sample Divider or Quartering with minimum mass as shown in Table 1:

Nominal size of material (mm)	40	28	20	14	10
Minimum mass of test portion (kg)	15	5	2	1	0.5

3.        

Dry the test portion in oven at (105±5) ^oC until constant mass, and then record M_o in (g).

·         Testing:

-          Place the test portion into container.

-          Discard all aggregates retained on 50.0 mm test sieve and Passing 6.30 mm.

-          Pour the residue on top of coarsest sieve and shake it manually or by mechanical shaker for sufficient time to separate into size fractions as in table 2:

Nominal size of test sieve (mm)	100% passing	50.0	37.5	28.0	20.0	14.0	10.0
	100% retained	37.5	28.0	20.0	14.0	10.0	6.30
Gaps between pins of gauge (mm)		78.7	59.0	43.2	30.6	21.6	14.7
Minimum mass of test portion (kg)		35	15	5	2	1	0.5

-           

-        

  Check the separation is complete by hand sieving.

-          Weigh the individual size-fractions retained on each sieve in (g).

-          Sum the masses of the fractions (M₁) in (g).

-          Calculate the individual percentage retained and discard fraction of less than 5%.

-          Record the remaining mass by (M₂) in (g).

-          Gauge each size-fraction by length gauge.

-          Combine all Elongated particles (not passing) and weigh (M₃) in (g).

·         Calculation:

-          Calculate the corrected mass of elongated particle (M₄) in (g) = (M₁/M₂) xM₃.

-          Calculate the % elongated particle (M₅) = (M₄/M₁) x100.

-          Calculate the value of Elongation Index = (M₅xM₁)/100.

-          Express Elongation Index to nearest whole number.