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IRC:SP:70-2005

GUIDELINES FOR THE USE OF HIGH PERFORMANCE CONCRETE IN BRIDGES

Published by

THE INDIAN ROADS CONGRESS
Kama Koti Marg,
Sector 6, R.K. Puram,
2005

Price Rs. 160/-
(Plus Packing & Postage )

PERSONNEL OF THE BRIDGES SPECIFICATIONS AND STANDARDS COMMITTEE
(As on 20-12-2004)

GUIDELINES FOR THE USE OF HIGH PERFORMANCE CONCRETE IN BRIDGES

1. INTRODUCTION

1.1.

The Reinforced, Prestressed and Composite Concrete Committee (B-6) of the Indian Roads Congress was reconstituted in 2003 with the following personnel:

1.2.

At its first meeting on 29^th April, 2003, the Committee felt that in the light of the massive construction programme that was under execution in the highway sector, it was necessary to bring out guidelines on certain topics which were not adequately covered in the existing IRC Codes and Standards. The guideline for the use of High Performance Concrete was one of the two topics selected. It was decided that the guidlines would be generally in line with IRC: 18 and IRC:21 with additional inputs from BS:5400, EURO and AASHTO codes, wherever necessary.

1.3.

The initial draft of the guidelines was prepared by Dr. A.K. Mullick. The draft was discussed by the B-6 Committee at several meetings and finalized in its meeting held on 3^rd September, 2004. The draft document was approved by Bridges Specifications and Standards Committee in its meeting held on 2^nd December, 2004 and by the Executive Committee on 18^th December, 2004. The document was considered by IRC Council in its 173^rd meeting held on 8^th January, 2005 in Bangalore and approved with certain modifications. The required modifications were accordingly carried out by the Convenor B-6 Committee before sending the document for publication.

2. SCOPE

High Performance Concrete (HPC) can be used both in super and substructure of bridges. The guidelines provide broad aspects for production of HPC including mix design. The guidelines on HPC should be read in conjunction with relevant IS and IRC Specifications and Codes of practice, besides International Codes/ Guidelines on the same topic, to gain confidence on its usage.1

3. TERMINOLOGY

3.1. High Performance Concrete

Concrete, whose ingredients, proportions and production methods are specifically chosen to meet special performance and uniformity requirements that cannot be always achieved routinely by using only conventional materials, like, cement, aggregates, water and chemical admixtures, and adopting normal mixing, placing and curing practices. These performance requirements can be high strength, high early strength, high workability, low permeability and high durability for severe service environments, etc. or combinations thereof. Production and use of such concrete in the field necessitates high degree of uniformity between batches and very stringent quality control.

4. MATERIALS

4.1. Cement

Any of the types of cement as per Table 1 may be used with the approval of the competent authority.

4.2. Mineral Admixtures

Any of the following mineral admixtures may be used as part replacement of Ordinary Portland Cement with the approval of the competent authority. Uniform blending with cement should be ensured by having dedicated facility and complete mechanised process control at the site to achieve specified quality.

4.2.1. Fly ash:

Conforming to Grade I of IS: 3812-3.The proportion should not be less than 20 per cent, nor should exceed 35 per cent by mass of cement.

4.2.2. Granulated Slag:

Ground granulated slag obtained by grinding granulated slag conforming to IS: 12089. The proportion should not be less than 50 per cent, nor should exceed 70 per cent by mass of cement.

4.2.3. Silica Fume:

Silica fume is very fine, non-crystalline SiO₂, obtained as a by-product of Silicon or Ferro-Silicon alloy industries. It should conform to IS: 15388.

4.3. Admixtures

Chemical admixtures and superplasticisers conforming to IS: 9103 may be used. Compatibility of the superplasticiser with the cement and any other pozzolanic or hydraulic additives as covered in Clause 4.2 being used,

should be ensured by trials, so that the following problems are avoided.

• Large dosage of superplasticiser required to achieve the desired workability,
• Excessive retardation of setting,
• Excessive entrainment of large air bubbles,
• Unusually rapid stiffening of concrete,
• Rapid slump loss, and
• Excessive segregation and bleeding.

4.4. Aggregates

4.4.1. General:

All coarse and fine aggregates shall conform to IS:383 and shall be tested as per IS:2386 Parts I to VIII.

4.4.2. Coarse aggregate:

Coarse aggregates shall consist of clean, hard, strong, dense, nonporous, equi-dimensional (i.e., not much flaky or elongated) and durable pieces of crushed stone, crushed gravel, natural gravel or a suitable combination thereof.

The maximum size of the coarse aggregate should not be greater than;

• one quarter of the minimum thickness of the member,
• 10 mm less than the minimum lateral clear distance between individual reinforcements,
• 10 mm less than the minimum clear cover to any reinforcement,
• Nominal maximum size of aggregate should not exceed 20mm.

4.4.3. Fine aggregate:

Fine aggregate shall consist of hard, strong, clean, durable particles of natural sand, crushed stone or crushed gravel. Suitable combinations of natural sand and crushed stone or crushed gravel can be permitted. They shall not contain dust, lumps, soft or flaky particles, mica or any other deleterious materials in such quantities as would reduce the strength or durability of concrete. Fine aggregate of Zone II or III of IS:383 are preferable.

4.5. Water

Water should conform to provisions of Clause 302.4 of IRC:21-2000.

4.6. Concrete

4.6.1. Strength grades of concrete:

The concrete shall be in grades designated in Table 2, where the characteristic strength is defined as the strength of concrete below which not more than 5 per cent of test results are expected to fall.

4.6.2.

The Cement content of concrete, inclusive of any mineral admixtures, shall be not less than 380 kg/m³.

4.6.3.

The Cement content excluding any mineral admixtures shall not exceed 450 kg/m³.

4.6.4.

The water/(cement+all cementitious materials) ratio should generally not exceed 0.33, but in no case more than 0.40.

4.6.5. Workability:

The concrete mix proportions chosen should be such that the concrete is of adequate workability for placing conditions and congestion of reinforcement, to ensure proper placement without segregation or honey combing, and thorough compaction.

Suggested ranges of workability of concrete measured in accordance with IS: 1199 are given below:3

4.7 Durability

4.7.1.

Concrete should be durable to provide satisfactory performance in the anticipated exposure conditions during service. The materials and mix proportions specified and used, and the workmanship employed should be such as to maintain its integrity and to protect embedded metal from corrosion.

4.7.2.

One of the main characteristics influencing the durability of concrete is its impermeability to the ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious substances. Impermeability is governed by the constituents and workmanship employed in making the concrete. A suitably low permeability is achieved by having an adequate cement content, sufficiently low water-cement ratio, dense packing of fine particles, by ensuring thorough compaction of the concrete, and by timely and adequate curing.

4.7.3.

Total water-soluble sulphate (SO₃) content of the concrete mix, expressed as (S0₃) shall not exceed 4 per cent by mass of cement used in the mix.

4.7.4.

Total chloride content in concrete, expressed as chloride-ion, shall not exceed the following values by mass of cement used:

4.8. Concrete Mix Design

4.8.1. General:

Choice of materials, concrete mix design and field practices are quite critical, so that optimum performance can be extracted of each of the ingredients. The procedure of mix proportioning of normal grades of concrete may not be adequate. Relationships between the compressive strength of concrete and water-cement ratio (or water-cement+cementious materials ratio, when part of the cement is replaced by mineral admixtures) and between water content and workability will have to be established by laboratory trials for the grade of concrete, the materials to be used, and the water-reducing efficiency of the superplasticiser.

4.8.2. Target mean strength:

The target mean strength of the mix should be equal to be characteristic strength for the grade plus the current margin.

4.8.2.1.

The current margin for a concrete mix shall be taken as 1.64 times the standard deviation of sample test results taken from at least 40 separate batches of concrete of nominally similar proportions produced at site by the same plant under similar supervision, over a period exceeding 5 days, but not exceeding 6 months.

4.5.2.2.

Where there are insufficient data to satisfy the above, the target mean strength for the initial mix design shall be taken as given in Table

3. As soon as the results of samples are available, actual calculated standard deviation may be used and the mix designed accordingly.

4.8.3. Field Trial Mixes:

Mix proportions arrived at by laboratory trials shall, in addition, be verified to be satisfactory under field conditions and necessary adjustments made. Field trial mixes shall be prepared for all grades of concrete, using samples of approved materials. Sampling and testing procedures shall be in accordance with para 4.11.

4.8.3.1.

The concreting plant and means of transportation employed to make trial mixes and to transport them to representative distances shall be similar to the corresponding plant and transport to be used in the works. The optimum sequence of mixing of ingredients shall be established by trials. Mixing time may be longer than in normal grade concrete mixes.

4.8.3.2.

The temperature of concrete at the time of placement shall not exceed 25°C. The temperature of concrete at the mixing stage should be lower, to allow for rise in temperature during transport. When considerable distance of transport is involved, particular attention should be paid to ensure retention of slump as targeted for placement.

4.8.4. Prototype testing:

Further mock-up trails or prototype testing may be carried out to ensure that the concrete can be satisfactorily placed and compacted, taking into account the location of placement and provision of reinforcement, and adjustments made in concrete mix design and/or detailing of reinforcement accordingly.

4.9. Production of Concrete

4.9.1. Batching an mixing:

Provisions of Clause 302.9.1 of IRC:21 shall apply. Fully automatic, computer controlled batching and mixing plant shall be used.

4.9.2. Curing:

High Performance Concrete containing silica fume is more cohesive than normal mixes hence, there is little or no bleeding and no bleed water to rise to the surface to offset water lost due to evaporation. Plastic shrinkage cracking is possible, if curing is not proper. Initial curing should commences soon after initial setting of concrete. Concrete should be covered with moist covers, opaque colour plastic sheets or suitable curing compound. Final moist curing should commence after final setting of concrete and continue for at least 14 days.

4.10. Quality Assurance

In order that the performance of the completed structure be consistent with the requirements and assumptions made during the planning and design, stringent quality assurance measures shall be taken. The construction should result in satisfactory strength, serviceability and long-term durability. In particular, it should be aimed to ensure uniformity and to lower the variability between batches of production, as evidenced by the standard deviation in test results.

The methods and procedures of Quality System shall be followed as per the guidelines contained in IRC:SP-47. Q-4 class of Quality Assurance shall be adopted for the ‘Materials’ and ‘Workmamship’ items.

4.11. Sampling and Testing

Provisions of Clause 302.10 of IRC:21 shall apply.

4.12. Acceptance Criteria

Provisions of Clause 302.11 of IRC:21 shall apply.

4.12.1.

Acceptance testing on site shall not be resticted to tests for compressive strength of concrete alone. Where durability of concrete is the main reason for adopting High Performance Concrete, Rapid Chloride Ion Permeability test as per ASTM C-1202 or AASHTO T-277 shall be carried out. The permissible value of chloride- ion permeability shall be less than 800 coulombs.

4.12.2.

Additional durability tests, such as, Water Permeability test as per DIN:1048 Part 5-1991 or Initial Surface Absorption test as per BS: 1881 Part 55

can also be specified. The permissible values in such tests shall be decided taking into account the severity of the exposure conditions.

5. BASIC PERMISSIBLE STRESSES IN CONCRETE

The properties and basic permissible stresses for concrete of grades upto M 60 shall be as given in Table 9 of IRC:21. For concrete of grades higher than M 60, properties of concrete, permissible stresses and design parameters given in IRC:18 and IRC:21 will not be applicable. Appropriate values may be obtained from specialized literature and/or International Codes of Practice.

REFERENCES

In this pulication reference to the following IRC, IS, BS, DIN Standards ASTM and AASHTO has been made. At the time of publication, the editions indicated were valid. All Standards are subject to revision and the parties to agreements based on these guidelines are encouraged to investigate the possiblitiy of applying the most recent editions of the Standards indicated below:

Codes and Specifications:

Papers and Publications