Requirements for Installing Saw Cut Joints
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Requirements for Installing Saw Cut Joints
Requirements for installation
For a smooth run and for the purpose of minimizing random concrete cracking in slabs, specifically on the ground. The structure has to be made the right way. Contraction joints allow unreinforced and feathery reinforced slabs on floors to reduce random cracking. Firstly, the panels formed by saw joints must be made square. Making them equitable is because a square shape allows better spacing. The joint layout is required to be divided into small shaped panels. For better crack control, one has to limit the length size to too small.
Secondly, the saw-cut joints should be continuous. Structural engineers recommend that the joint in serial form allow cracking to continue into the enjoined concrete, which is the difference between it and discontinuous joints. Also, another requirement is that the operator looks at and addresses re-entrant corners. This is also to control cracking that starts there. The engineer must also install contraction joints where slabs typically begin to break. Installations of this cut joint are essential to understanding typical crack locations. To have thicker slabs, the saw-cut joints are supposed to be increased to ensure joint activation. The timing of saw cut joint installation is vital. Saw common cuts must be sawed immediately after the concrete has supported the energy of sawing with dislodging particles. The mixture should be sawed for approximately seven to nineteen hours and not more than 24 hours.
The saw cut time is dependent on the weather too. As soon as everything is in order, Timing well entry joint saw cutting offers several long-term performance benefits. Changes in moisture and temperature conditions have an impact on saw-cut joints. According to a study by Chon and Lee (2017), the saw cuts have been categorized into two patterns, prior mid-slab cracking pattern and low tensile stress pattern. The first pattern occurs before the saw cut at joints, and joints have not yet cracked. The other designates that some parts of the joint are broken, and others are not. The operators have to create straight-line weak planes in concrete, and the control joints help to set the cracking location by inducing cracks at the initial determined segment. The slab has to shrink because of cooling and drying; as this happens, shrinkage starts building, and cracks form at contraction joints because the concrete has been made weak at these locations.
Fig 1: mega saw, concrete cutting.
The primary reason for saw joints cuts has been said is to encourage shrinkage restraints cracking at pre identified locations. The joint has been controlled to serve its initial objective. Saw cutting have been found to provide joint nosing and allows a semi-joint filler to be installed.
Techniques for installing Saw Cut Joints
As discovered before, the timing to make control joints is an essential aspect of the proper use of control joints. Some of the things to consider while designing proper techniques are the concrete mix, hardness, and types of machines to use for making control saw joints when cutting the slab. The technique here is known as the raveling technique. The raveling technique involves setting time. Timing when to install the joints is essential. Sawing without proper time techniques may result in uncontrolled cracking as the concrete can contract during the curing process. Recent studies conducted have provided proper findings that saw proper cutting provides window opportunities. The timing determined occurs and depends on the rate of strength development in the concrete. Efficient timing is advantageous to the joint depth because can be reduced and still result to joint activation (Min et al, 2022).
Another important technique for saw cuts is the proper location. The experts in this field have stated that control joints should be placed at the center of the slab dividing the concrete into equal parts. The spacing is supposed to be in a range of 23 to 38 times the thickness of the slab. Some of the things to look for in the location of the cut are continuity, and they must have square patterns, the steel reinforcement should be less, and the segment of the proper size. The size of the slab has been proven to enable the convectional pieces to be larger due to the easy setting of the concrete in a big area.
Fig 2: Master joint concrete website.
The third installation technique is determining the depth of the control joint, and you have to cut the joints ¼ to 1/3 the slab thickness. The slab concrete must be about 150 millimeters thick, and the depth of the slab cut joint is around 45mm.The importance of depth technique is that it helps protect the joint from heavy wheeled traffics. The main purpose of this saw cut is to control random cracking. The studies on depth of saw joint cutting have shown that the cut depends on the crack’s strength of the concrete and it’s much important that saw cut in controlling random cracking. Saw cut depth depends on the concrete’s strength and the saw cut timing is more vital compared to saw cut depth when it comes to controlling cracking.
Reference
Chon, B.J., Lee, and S.W. Effects of uncracked joints in jointed concrete pavements. KSCE J Civ Eng. 11, 141–144 (2017). https://doi.org/10.1007/BF02823893Min, Z., Wang, Q., Zhang, K., Shen, L., Lin, G., & Huang, W. (2022). Investigation on the properties of epoxy asphalt mixture containing crumb rubber for bridge expansion joint. Construction and Building Materials, 331, 127344.
