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Concrete In Australia : September 2011
Concrete in Australia Vol 37 No 3 29 4. Jack western end as per step 3. 5. Jack parallel to the joint again. Jack to failure of the hammerhead occurs or slabs have displaced longitudinally 20 mm. Measure load and displacement of slabs at regular intervals. Jacking procedure for Test Slabs 2, 3, 4 and 5 1. All jacking used a hydraulic hand pump (for slow, controlled application of load). 2. Seven days after grouting, slabs were jacked apart. Loads and displacement were recorded at regular jacking intervals. e pressure and force in both jacks was kept the same throughout the jacking (calibration revealed less than 2% difference). Maximum jack load was based on yielding of the bars and was not to exceed the total of 232 kN in each jack. 3. To check the layers of plastic did not increase the apparent resistance of the sleeves (and therefore yield unconservative test results), on two slabs the reinforcement bars were sawn, then the two pours jacked apart. 4.0 OBSERVATIONS DURING GROUTING OF TEST SLAB 1 During grouting of the individual sleeves on the southern joint the following was observed: • For Type 1 sleeves (single grout tube at one end only) -- Six sleeves had grout flowing into the joint, however two sleeves had no flow observed into the joint. It is expected that these sleeves are blocked and as there is no bleeder tube then it was also expected that these sleeves would not be filled with grout. -- e remaining 5 sleeves had good flow of grout into the joint. • For type 2 sleeves (a single grout tube at both ends) -- Two sleeves did not have any grout flowing into the joint. However, as there was a bleeder tube close to the joint, the grout filled the sleeve and flowed out the bleeder tube. -- For another two sleeves, grout flowed readily into the joint, but no grout came out of the bleeder tube. It is expected that there was no blockage in these sleeves. -- For the remaining three sleeves, grout ran out of both the bleeder tube and into the joint. It is expected that these sleeves were partially blocked, resulting in some flow into the joint and some flow out of the sleeve. • For type 3 sleeves (two grout tubes at one end) -- For all sleeves, grout was observed flowing into the joint and no grout flowed out of the bleeder tube. As no grout flowed out of the bleeder tube it is expected that none of these sleeves were completely blocked at the joint end, thus the effectiveness of having a bleeder tube next to the grouting tube is not fully tested. • While grouting, grout filled the joint completely around the sleeve being grouted and ran along the joint. When grouting was stopped on each sleeve, the grout continued to run along the joint such that the level of the grout in the joint lowered considerably. As the grout level lowered below the level of the sleeve air is able to enter the sleeve. e first sleeves grouted needed to be re-grouted twice to ensure the sleeve remained filled. On re-grouting, bubbles of air were clearly visible coming out of the sleeve. • Considerable grout comes out the top of the joint when grouting as this is the path of least resistance. As the grout tends to run faster out of the top of the joint than it does flowing along the joint, this causes pooling of grout on the surface of the slab. Best results were obtained by slowing the speed of the grout from the grout pump such that it filled the joint slowly. Grouting of the looped sleeves on the northern joint occurred from the eastern grout vent. Grout was observed flowing readily out of the first sleeve into the joint and ran readily along the joint. No grout was observed coming out of any of the other sleeves into the joint. After 5 minutes, the joint was approximately half full in the middle and one quarter filled at west end. Unfortunately, there was grout leaking from under the slab and through a section of the slab that failed in bearing. As a result of the leak, the joint was unable to be filled from the eastern end. Grouting then commenced from the western end however as the grout leaking from under the slab at the western end was considerable then filling the northern joint was not successful. As a result of the leak, it was expect that the majority of the northern sleeves would no be filled. 5.0 TEST RESULTS 5.1 Resistance to sliding -- Test Slab 1 It was intended that when jacking Test Slab 1 the force required to slide the sleeves over the bar could be measured both perpendicularly to the joint as well as parallel. Unfortunately this was not the case and no reliable results could be obtained. When jacking perpendicularly to the joint, the force required for first movement of the slab was completely different on the north and south side of the joint. For the south side the joint could be opened up to 5 mm each end, however there was no gap in the middle and when the loads in the jacks were released the gap closed again. An intermediate "spreader" jack was required to open the joint in the middle and obtain a continuous gap along the joint. Whilst using the spreader jack both the east and west ends were also jacked apart and the load held such that there was in excess of 0.5 t per sleeve resistance to perpendicular movement. is force is substantial considering the sleeves can be slid on by hand with ease prior to concreting. When jacking longitudinally, a total of 25 t of force was applied to move the slabs 4 mm. is is again in excess of 0.5 t of sliding resistance per sleeve. Once the jack load was released the slabs moved back to their original unloaded position. e hammerhead failed at 25 t. e jacking created a 10 mm minimum continuous gap along both the north and the south joint. 5.2 Grouting method -- Test Slab 1 As mentioned above, the slab was cut after grouting in order