ITEM 708 – CHEMICAL ADMIXTURES FOR CONCRETE

708.1 Description

This Item specifies the classification, sampling, testing, packing and marking of concrete admixtures. It also specifies the physical requirements for concrete with each type of chemical admixtures.

Admixtures              -A material, other than water, aggregates and hydraulic cement (including blended cement) that is used as an ingredient of concrete and is added to the batch in controlled amounts immediately before or during mixing to produce some desired modification to the properties of the concrete.

708.2 Types of Chemical Admixtures for Concrete

The concrete chemical admixture shall be classified as follows and shall conform to the requirements of AASHTO M 194.

a. Type A – Accelerating Admixtures

An admixture that accelerates the time of setting and early strength development of concrete.

b. Type B – Retarding Admixtures

An admixture that delays the time of setting of concrete.

c. Type C – Water-reducing Admixtures

An admixture that reduces the quantity of mixing water required to produce concrete of a given consistency.

            d. Type D – Water-reducing High Range, Admixtures

An admixture that decreases the quantity of mixing water required to produce concrete of a given consistency by 12 percent or greater.

e. Type E – Water-Reducing and Accelerating Admixtures

An admixture that decreases the quantity of mixing water required to produce concrete of a given consistency and hastens the time of setting and early strength development of concrete.

f. Type F – Water-Reducing and Retarding Admixtures

An admixture that decreases the quantity of mixing water required to produce concrete of a given consistency and delays the time of setting of concrete.

g. Type G – Water-Reducing, High Range, and Retarding Admixtures

An admixture that decreases the quantity of mixing water required to produce concrete of a given consistency of 12 percent or greater and delays the time of setting of concrete.

708.3 Air-Entraining Admixtures

Air-entraining admixtures shall conform to the requirements of AASHTO M 154 (ASTM C 260).

708.4 Physical Requirements 

The concrete in which each of the types of chemical admixtures are used shall conform to the physical requirements given in Table 1.

Table1–Physical Requirements of Chemical Admixtures for Concrete^A

PHYSICAL PROPERTY	Type A	Type B	Type C	Type D	Type E	Type FB	Type GB
Water Content, percent of control, maximum	95	-	-	95	95	88	88
Time of setting, allowable deviation from control, hour
Initial Minimum	-	1.0 later	1.0 earlier	1.0 later	1.0 earlier	-	1.0 later
Maximum	1.0 earlier nor 1.5 later	3.5 later	3.5 earlier	3.5 later	3.5 earlier	1.0 earlier nor 1.5 later	3.5 later
Final : Minimum	-	-	1.0 earlier	-	1.0 earlier	-	-
Maximum	1.0 earlier nor 1.5 later	3.5 later	-	3.5 later	-	1.0 earlier nor 1.5 later	3.5 later
Compressive Strength, percent of control minimum:C
1 day	-	-	-	-	-	140	125
3 days	110	90	125	110	125	125	125
7 days	110	90	100	110	110	115	115
28 days	110	90	100	110	110	110	110
6 months	110	90	90	100	100	100	100
1 year	100	9	90	100	100	100	100
Flexural Strength, percent of control, minimum:C
3 days	110	90	110	100	110	110	110
7 days	100	90	100	100	100	100	100
28 days	100	90	90	100	100	100	100
Length Change, maximum shrinkage (Alternative requirements)D Percent of control	135	135	135	135	135	135	135
Increase over Control	0.010	0.010	0.010	0.010	0.010	0.010	0.010
Relative durability factor minimum	80	80	80	80	80	80	80

^A              The values in the table include allowance for normal variation in test results. The objects of the 90% compressive strength for Type B admixture is to require a level of performance comparable to that of the reference concrete.

^B              It is recommended that whenever practicable, tests may be made using cement, pozzolan, aggregates, air-entraining admixture, and the mix proportions and batching sequence when used in non-air-entraining and air-entrained concrete because the specific effects produced by chemical admixtures may vary with the properties and proportion of the other ingredients of the concrete. For instance, types “F” and “G” admixtures may exhibit such higher water reduction in concrete mixtures having higher cement factors than 307 ±3 kg/m³. Mixtures having a high range water reduction generally display a higher rate of slump loss. When high range admixtures are used to impart increased workability (15 cm to 20 cm slump), the effect may be of limited duration, reverting to the original slump in 30 to 60 min depending on factors normally affecting rate of slump loss.

^C              The compressive and flexural strength of the concrete containing the admixture under test at any test age shall be not less 90% of that attained at any previous test age. The objective of this limit is to require that the compressive or flexural strength of the concrete containing the admixture under test shall not decrease with age.

^D              The percent of control limit applies when length change of control is 0.030% or greater; increase over control limit applies when length change of control is less than 0.030%.

^E              This requirement is applicable only when the admixtures is to be used in air-entrained concrete.

When the admixture is to be used in Prestressed concrete, the chloride content of the admixture shall be stated and whether or not chloride has been added during its manufacture.

708.5 Sampling 

708.5.1           The chemical admixtures for concrete shall be sampled either by grab or composite sampling. A grab sample is one obtained in a single operation. A composite sample is one obtained by combining three or more grab samples.

708.5.2 Liquid Admixtures

708.5.2.1        The grab samples taken for quality tests shall represent a unit shipment or a single production lot. Each grab sample shall have a volume of at least 0.5L, a minimum of 3 grab samples shall be taken.

708.5.2.2        Liquid admixtures shall be agitated thoroughly immediately prior to sampling. Grab samples shall be taken from different locations and thoroughly mixed to form the composite sample and the resultant mixture sampled to provide for at least 4 liters for complete set.

708.5.2.3        Admixtures in bulk storage tanks shall be sampled equally from the upper, intermediate and lower levels by means of drain cocks in the sides of the tanks or a weighed sampling bottle fitted with a stopper that can be removed after the bottle is lowered to the proper depth.

708.5.3 Non-liquid Admixtures

708.5.3.1        The grab samples taken shall represent not more than 2 tons of admixture and shall have a mass of at least 1 kg. A minimum of four grab samples shall be taken.

708.5.3.2        Composite samples shall be prepared by thoroughly mixing the grab samples selected and the resultant mixture sampled to provide at least 2.3 kg for complete test.

708.6 Testing 

Procedures for Proportioning of Concrete Mixtures, Tests and Properties of Freshly Mixed Concrete, Preparation of Test Specimens, Test Specimens of Hardened Concrete and Tests on Hardened Concrete shall be in accordance with AASHTO M 194.

The Concrete containing the admixtures shall be tested in accordance with ASTM C 39, ASTM C 138, ASTM C 192, ASTM C 617.

708.7 Packing 

The liquid admixtures shall be packed in 4, 20 or 200-liter containers made of steel, plastic or other suitable packing materials. These containers shall be properly sealed.

The non-liquid admixtures or concrete shall be packed in 25-kilogram containers made of steel, plastic, or other suitable packing materials. These containers shall be properly sealed.

708.8 Marking 

Each container shall be marked with the following information:

a. Name, form and type of the product;

b. Net mass or volume;

c. Name and address of manufacturer and recognized trademark, if any;

d. Manufacturer’s batch number and date of manufacture

e. Made in the Philippines and,

f. Required handling procedures