A-1.1 The Position of Construction Joints
A-1.1.1 Construction joints should be positioned to minimise the effect of the discontinuity on the durability, structural integrity and appearance of the structure.
A-1.1.2 As far as possible, joints should be positioned in non-aggressive zones, but if aggressive zones cannot be avoided, joints should be sealed.
A-1.1.3 Joints should be positioned where they are readily accessible for preparation and concreting, the preparation of the joints is more likely to be satisfactory where the cross section is relatively small and where reinforcement is not congested.
A-1.1.4 As far as possible, joints for fairfaced concrete should be located where they conform with the architectural features of the construction. Unless they are masked in this way, the position of the joints are always obvious, even when the concrete is given a textured finish.
A-1.1.5 If substantial changes in the cross section of a member are necessary, the joints should be formed where they minimise stresses caused by temperature gradients and shrinkage.
A-1.1.6 Joints should be located away from regions of maximum stress caused by loading, particularly where shear and bond stress are high. Construction joints between slabs and ribs in composite beam should be avoided. As a general rule, joints in column are made as near as possible to the beam hunching, joints in beams and slabs should normally be made at the centre or within the middle third of the span.
A-1.2 Preparing the surface of the Joint
A-1.2.1 The minimum number of joints should be used and their construction should be simple. They should be either horizontal or vertical, because concreting sloping surfaces are usually unsatisfactory.
A-1.2.2 Where concrete is placed in vertical members e.g. walls, columns and the like, the lift of concrete shall finish level or at right angles to the axis of the member, the joint line matching the features of the finished work.
Concreting shall be carried out continuously upto the construction joint.
A-1.2.3 Laitance, both on the horizontal and vertical surfaces of the concrete, should be removed before fresh concrete is cast. The surface should be roughened to promote good adhesion. Various methods for removal can be used but they should not dislodge the coarse aggregate particles. Concrete may be brushed with a stiff brush soon after casting while the concrete is still fresh, and while it has only slightly stiffened.
A-1.2.4 If the concrete has partially hardened, it may be treated by wire brushing or with a high pressure water jet, followed by drying with an air jet, immediately before the new concrete is placed.
A-1.2.5 Fully hardened concrete should be treated with mechanical hand tools or grill blasting, taking care not to split or crack aggregate particles.
A-1.2.6 The best time for treating the joint is a matter of judgment because it depends on the rate of setting and hardening (which is itself dependent on the temperature of the concrete). Before further concrete is cast, the surface should be thoroughly cleaned to remove debris and accumulated rubbish, one effective method, being air jet.
A-1.2.7 Where there is likely to be a delay before placing the next concrete lift, protruding reinforcement should be protected. Before the next lift is placed, rust, loose mortar or other contamination should be removed from the bars and where conditions are particularly aggressive and there has been a substantial delay between lifts, the concrete should be cut back to expose the bars for a length of about 50mm to ensure that contaminated concrete is removed.
A-1.2.8 In all cases, when construction joints are made, to essential it is ensure that the joint surface is not
A-1.3.2 The practice of first placing a layer of mortar or grout is not recommended. The old surface should be soaked with water without leaving puddles, immediately before starting concreting,; then the new concrete should be thoroughly compacted against it. When fresh concrete is cast against existing mature concrete or masonary, the older surfaces should be thoroughly cleaned and soaked to prevent the absorption of water from the new concrete. Standing water should be removed shortly before the new concrete is placed and the new concrete should be thoroughly vibrated in the region of the joint.
contaminated with release agents, dust or curing membrane, and that the reinforcement is fixed firmly in position at the correct cover.
A-1.3 Concreting at Construction Joints
A-1.3.1 When the form work is fixed for the next lift, it should be inspected to ensure that no leakage can occur from the fresh concrete. It is a good practice to fix a 6mm thick sponge which seals the gap completely.
Appendix-B ( CLAUSE 7.2.6.4.2.4) TESTS ON SHEATHING DUCTS
FIG B-3: TENSION LOAD TEST
B-7.1 For working out the volume, another sample 500mm long is sealed at one end and the volume of hollow space is arrived at by pouring water from a measuring cylinder. The computation of relative profile volume is worked out as follows
:-Relative Profile Volume = cm/cm L
π L/4 π
V 2 3
p
I I
L - Length of the specimen
I
- nominal internal diameter of the sheathingVa - premeasured quantity of water in a measuring cylinder.
Vb - balance quantity of water left in the cylinder after completely filing of the test sample.
Actual volume Vp =Va - Vb
FIGURE B-4 : TEST FOR WATER LOSS STUDY B-1 All tests specified below shall be carried out on the
same sample in the order given below.
B-2 At least 3 samples for one lot supply ( not exceeding 7000m length) shall be tested.
B-3 The tests are applicable for sheathing transported to site in straight lengths where the prestressing tendon is threaded inside the sheathing prior to concreting. These tests are not applicable for sheathing and cable coiled and transported to site as an assembled unit, nor for sheathing ducts placed in position without threading of prestressing cable prior to concreting.
B-4 WORKABILITY TESTS – A test sample of 1100 mm long is soldered to a fixed base plate with a soft solder (Fig.
B1). The sample is then bent to a radius of 1800mm alternatively on either side to complete 3 cycles. Thereafter, the sealing joints will be visually inspected to verify that no failure or opening has taken place.
B-5 TRANSVERSE LOAD RATING TEST - The test ensures that stiffness of the sheathing is sufficient to prevent permanent distortion during site handling.
B-5.1 The sample is placed on a horizontal support 500mm long so that the sample is supported at all points of outward corrugations. A load as specified in Table B1 is applied gradually in increments at the centre of the supported portion through a circular contact surface of 12mm dia.
Couplers shall be placed so that the load is applied approximately at the centre of two corrugations (Fig. B-2).
The sample is considered acceptable if the permanent deformation is less than 5 percent.
B-6 TENSION LOAD TEST- The test specimen is subjected to a tensile load. The hollow core is filled with a wooden circular piece having a diameter of 95 percent of the inner diameter of the sample to ensure circular profile during test loading ( Fig. B-3). A coupler is screwed on and the sample is loaded in increments, till load specified in Table B-2. If no deformation of the joints nor slippage of couplers is noticed, the test shall be considered satisfactory.
B-7 Water Loss Test – The sample is sealed at one end. It is then filled with water. After the other end is also sealed as shown in Fig. B-4, it is connected to a system capable of applying a pressure of 0.05N/mm2 and kept constant for 5 minutes. The same is acceptable if the loss of water does not exceed 1.5 percent of the volume.
TABLE B-1: TENSION LOAD TEST (Clause B-5)
DIAMETER OF SHEATHING(d)
(mm) LOAD(F)
(N) For MS