Chapter 16Inspection and Testing of Structures

16.1 Inspection

To ensure that the construction complies with the design an inspection procedure should be set up covering materials, records, workmanship and construction.

16.1.1 Tests should be made on reinforcement and the constituent materials of concrete in accordance with the relevant standards. Where applicable, use should be made of suitable quality assurance schemes.

16.1.2 Care should be taken to see that,

a) design and detail are capable of being executed to a suitable standard, with due allowance for dimensional tolerances;

b) there are clear instructions on inspection standards;

c) there are clear instructions on permissible deviations;

d) elements critical to workmanship, structural performance, durability and appearance are identified; and

e) there is a system to verify that the quality is satisfactory in individual parts of the structure, especially the critical ones.

16.2 Immediately after stripping the formwork, all concrete shall be carefully inspected and any defective work or small defects either removed or made good before concrete has thoroughly hardened.

16.3 Testing

In case of doubt regarding the grade of concrete used, either due to poor workmanship or based on results of cube strength tests, compressive strength tests of concrete on the basis of 16.4 and/or load test (see 16.6) may be carried out.

16.4.1 The points from which cores are to be taken and the number of cores required shall be at the discretion of the Engineer-in-Charge and shall be representative of the whole of concrete concerned. In no case, however, shall fewer than three cores be tested.

16.4.2 Cores shall be prepared and tested as described in accepted standard [6-5A(14)].

16.4.3 Concrete in the member represented by a core test shall be considered acceptable if the average equivalent cube strength of the cores is equal to at least 85 percent of the cube strength of the grade of concrete specified for the corresponding age and no individual core has a strength less than 75 percent.

16.5 In case the core test results do not satisfy the requirements of 16.4.3 or where such tests have not been done, load test (see 16.6) may be restored to.

16.6.1 Load tests should be carried out as soon as possible after expiry of 28 days from the time of placing of concrete.

16.6.2 The structure should be subjected to a load equal to full dead load of the structure plus 1.25 times the imposed load for a period of $24\mathrm{h}$ and then the imposed load shall be removed.

NOTE — Dead load includes self weight of the structural members plus weight of finishes and walls or partitions, if any, as considered in the design.

16.6.3 The deflection due to imposed load only shall be recorded. If within 24 h of removal of the imposed load, the structure does not recover at least 75 percent of the deflection under superimposed load, the test may be repeated after a lapse of 72 h. If the recovery is less than 80 percent, the structure shall be deemed to be unacceptable.

16.6.3.1 If the maximum deflection in mm, shown

during $24\mathrm{h}$ under load is less than $40\left(\frac{l^2}{D}\right)$, where $l$ is the effective span in $\mathfrak{m}$; and $D$, the overall depth of the section, in mm, it is not necessary for the recovery to be measured and the recovery provisions of 16.6.3 shall not apply.

16.7 Members Other Than Flexural Members

Members other than flexural members should be preferably investigated by analysis.

Non-destructive tests are used to obtain estimation of the properties of concrete in the structure. The methods adopted include ultrasonic pulse velocity and rebound hammer {see accepted standards [6-5A(34)]}, probe penetration, pullout and maturity. Non-destructive tests provide alternatives to core tests for estimating the strength of concrete in a structure, or can supplement the data obtained from a limited number of cores. These methods are based on measuring a concrete property that bears some relationship to strength. The accuracy of these methods, in part, is determined by the degree of correlation between strength and the physical quality measured by the non-destructive tests.

Any of these methods may be adopted, in which case the acceptance criteria shall be agreed upon prior to testing.

16A Self Compacting Concrete

16A.1 General

The Self Compacting Concrete (SCC) is highly flowable, non-segregating concrete that fills uniformly and completely every corner of formwork by its own weight without the need for any compaction and encapsulates reinforcement or any other embedment. The provisions relating to its application areas, features, mix proportioning principles, and production and engineering properties are given hereunder. The provisions for concrete making materials and concrete as given in Section 5A (B1) ‘Materials, Workmanship, Inspection and Testing’ shall apply to SCC except where different provisions or departures have been indicated hereunder.

SCC may be used in in-situ concrete or for precast concrete applications. It is particularly appropriate for sections with highly congested reinforcement such as, nuclear power plant structures, machine foundations, piers and abutments; and areas having restricted access

PART 6 STRUCTURAL DESIGN — SECTION 5 CONCRETE: 5A PLAIN AND REINFORCED CONCRETE

to concrete placement and compaction like shafts in hydropower structures. SCC is also suitable for the construction of tunnel lining sections and casting of concrete-filled steel tubular columns. SCC may also be used for columns and beams in normal construction with appropriate formwork design.

SCC may be produced in a batching plant on site or in ready-mixed concrete plant and transported to site by transit mixers. It may be placed either by pumping or other placement methods into horizontal or vertical forms.

16A.3 Features of Fresh Self Compacting Concrete

The features of fresh SCC are:

a) Filling ability (Flowability),

b) Passing ability,

c) Segregation resistance, and

d) Viscosity.

16A.3.1 Filling Ability (Flowability)

Filling ability of SCC determines its ability to flow into and fill all spaces within the formwork, under its own weight. The filling ability is tested using slump-flow test.

16A.3.1.1 Procedure

Slump flow test shall be carried out in accordance with accepted standard [6-5A(20)].

There are three classes of slump-flow, as follows:

a) $SF1$ (slump flow $550~mm - 650~mm$) — This class of SCC is appropriate for,

1. unreinforced or slightly reinforced concrete structures that are cast from the top with free displacement from the delivery point (such as slabs),

2. casting by a pump injection system (such as tunnel linings), and

3. sections those are small enough to prevent long horizontal flow (for example, piles and some deep foundations).

b) SF2 (slump flow 650 mm - 750 mm) is suitable for many normal applications (for example, walls, columns)

c) SF3 (slump flow 750 mm - 850 mm) is typically produced with a small maximum size of aggregates (less than 20 mm) and is used for vertical applications in structures having congested reinforcement, structures with complex shapes, etc. SF3 will often give better surface finish than SF2 for normal vertical applications but segregation resistance is more difficult to control.

Passing ability describes the capacity of the fresh mix to flow through confined spaces and narrow openings such as areas of congested reinforcement without segregation. If there is little or no reinforcement, there may be no need to specify passing ability as a requirement. L-box test is generally carried out to check the passing ability and the procedure shall be in accordance with accepted standard $[6-5\mathrm{A}(20)]$ . In this test, the height of the concrete left in the vertical section $(h_{1})$ and at the end of the horizontal section $(h_{2})$ is measured. The ratio of $h_{2}/h_{1}$ is calculated as the blocking ratio; which shall be between 0.8 and 1.0.

16A.3.3 Segregation Resistance (Stability)

Segregation resistance is the ability of fresh concrete to remain homogeneous in composition while in its fresh state. Segregation resistance is generally carried out using sieve test to check this property of fresh concrete.

16A.3.3.1 Procedure

Segregation resistance (sieve) test shall be carried out in accordance with accepted standard [6-5A(20)].

There are two classes of segregation resistance, namely SR1 and SR2. For SR1 class, segregation resistance should be above 15 percent and ≤ 20 percent, and for SR2 it should be ≤15 percent.

SR1 is generally applicable for thin slabs and for vertical applications with a flow distance of less than 5 m and a confinement gap greater than 80 mm. SR2 is preferred in vertical applications if the flow distance is more than 5 m with a confinement gap greater than 80 mm in order to take care of segregation during flow. Segregation resistance becomes an important parameter with higher slump-flow classes and/or the lower viscosity class, or if placing conditions promote segregation. If none of these apply, it is usually not necessary to specify a segregation resistance class.

16A.3.4 Viscosity

Viscosity can be assessed by the V-funnel flow time. Concrete with a low viscosity will have a very quick initial flow and then stop. Concrete with a high viscosity may continue to creep forward over an extended time.

16A.3.4.1 Procedure

Viscosity by V-funnel test is carried out in accordance with accepted standard [6-5A(20)]. A V-shaped funnel is filled with fresh concrete and the time taken for the concrete to flow out of the funnel is measured and recorded as the V-funnel flow time.

The viscosity is divided into two classes, namely $V1$ and $V2$. For $V1$ class, the time taken to pass the concrete from V-funnel shall be $\leq 8$ s and for $V2$ class, it shall be above $8$ s and $\leq 25$ s.

V1 has good filling ability even with congested reinforcement. It is capable of self-levelling and generally has excellent surface finish. V2 class viscosity is more likely to exhibit thixotropic effects, which may be helpful in limiting the formwork pressure or improving segregation resistance. But it may cause negative effects on surface finish and sensitivity to stoppages or delays between successive lifts.

16A.4 Mix Proportioning

16A.4.1 Mix Proportion Principles

The principles listed below shall be followed:

a) Lower coarse aggregate content;

b) Increased paste content;

c) Low water/powder ratio (see Note);

d) High range superplasticizer; and

e) Viscosity modifying admixture, if required.

NOTE — Powder is the material of particle size smaller than 0.125 mm. It includes this size fraction in the cement, mineral admixtures and aggregate.

16A.4.2 Mix Design Procedure

For mix design procedure, reference may be made to good practice [6-5A(35)].

16A.5 Production of Self Compacting Concrete

16A.5.1 General

SCC is less tolerant to changes in constituent characteristics and batching variances as compared to conventional concrete. Accordingly, it is important that all aspects of the production and placing processes are carefully supervised.

The production of SCC should be carried out in plants where the equipment, operation and materials are suitably controlled under a Quality Assurance Scheme. It is important that all personnel who will be involved in the production and delivery of SCC are adequately trained including practical demonstrations.

SCC is more sensitive than conventional concrete to variation in the physical properties of its constituents and especially to changes in aggregate moisture content, grading and shape. So, more frequent production checks are necessary. The moisture content of aggregates should be continuously monitored and the mix adjusted

to account for any variation.

Storage of constituent materials for SCC shall be same as that for materials for conventional concrete. However, as the SCC mix is more sensitive to variations, special precautions shall be taken for storage of aggregates, which should be properly stored to avoid cross-contamination between different types and sizes and protected from weather to minimise the fluctuation of surface moisture content and movement of fines. Ground stock should be stored in purpose-built partitioned bays, which should allow free drainage of excess moisture in the aggregates and rainwater.

16A.5.3 Mixing Equipment and Trial Mixes

SCC shall be produced with efficient forced action concrete mixers. The time necessary to achieve complete mixing of SCC may be longer than for conventional concrete due to reduced frictional forces and to fully activate the superplasticizer.