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[Audio] Good evening everyone. Today, I am pleased to talk to you about an important technical discipline in the field of stone masonry, which is the repair of stone masonry. We will focus on two specific aspects: making "Through Bond" in random rubble masonry and connecting two existing stone walls. Let's look further into the specifics of this discipline..
[Audio] To construct a through bond in random rubble masonry, select a location in the wall with a one-meter horizontal and vertical distance. Remove the plaster from the area as well as the mortar around the stones, then carefully remove the stone from the wall to create a hole of around 75mm. Insert an 8mm diameter M S bar with hooks into the hole and fill it with 1:2:4 concrete. Finally, cure the surface by sprinkling it with water for 10 days..
[Audio] Using the "Making Through Bond in Random Rubble Masonry Wall" technique, two existing stone walls can be strengthened by stitching together at the corners. To do so, two 20mm diameter holes must be drilled into the masonry at a 45° angle. The depth of the hole in the longitudinal wall should be up to two times the thickness of the cross wall. Following this, a 10mm diameter steel bar should be inserted into the hole and filled with cement grout..
[Audio] Repair of stone masonry walls is necessary, as these constructions are particularly vulnerable to delamination and complete collapse. In order to strengthen them, internal impregnation of a rich cement grout or covering with steel mesh and mortar is necessary. To begin, two to four holes are drilled per square meter area, then cleaned and cement-sand grout is injected at a pressure of 0.1 to 2.5 MPa from the bottom to the top. If the wall contains numerous cracks on both sides, wire mesh should be fixed to it with steel rods at a distance of 300 to 400 mm and a cement mortar is used to complete the surface. For thicker walls, ‘Through Stone’ or ‘Through Bond’ should be placed at 1/3 points in the length and height. Longer walls must be reinforced with a buttress..
[Audio] We have been discussing how to repair walls to prevent dampness. Firstly, we need to understand the concept of plinth, which is the portion of the wall immediately above the ground level to the ground floor level, typically ranging from 45 cm to 100 cm in height. A damp proof course (DPC) is often added to prevent dampness from the foundation reaching the walls through capillary action of ground water. It should be 40 mm to 50 mm thick, made with a 1:2:4 cement concrete mix and a waterproofing compound. In some cases, a 100 mm thick plinth beam reinforced with bars is provided at the plinth level. When repairing these walls, two approaches are used: providing a new DPC layer and pressure injection of resin mortar in holes..
[Audio] Without greetings, without beginning with Today, and without thanks: I'm going to explain how to repair stone masonry - specifically, how to create 'through bond' connections between existing rubble walls. For installing a new DPC layer in an older building, which was built without a DPC, we cut the mortar bed of the two brick courses above ground level. This is a slow process and may lead to structural settlements and crack formation, so it is rarely used. An alternative is to drill inclined holes in the plinth portions of the walls and inject water soluble silicon. Additionally, silicon paint can be used to waterproof the exterior walls, in order to prevent rainwater from entering the walls. These injections can be done either with pressure or gravity-fed methods..
[Audio] Removing the plaster up to three to four brick layers above ground level is the first step of the method of repair for stone masonry walls involving 'Through Bonds'. 12 mm diameter holes are bored into the walls up to 2/3t thickness and chemical solutions are injected. For the water-based solution, it is a low-pressure injection and for the solvent-based solution, it is a high-pressure injection. Holes are then finished with waterproof mortar. An alternative method of repair is also outlined in this slide which is the gravity feed method. 25mm diameter inclined holes are drilled into a wall up to 2/3t thickness. Tubes are inserted and chemicals are transfused from containers under gravity until the masonry is saturated..
[Audio] We will be discussing the repair of stone masonry walls. To create a connection between existing stone walls, 20mm to 30mm diameter holes should be bored at a depth of 3/5t in a wall from both sides and the c/c spacing of the holes should be 30cm. The holes should be inclined downwards at an angle of 20° to 30°. After drilling, flush out the holes and inject a special mortar composed of cement, styrene butadiene resin or epoxy resin, mixed according to the instructions given by the manufactures. The resin hardens and creates an impervious layer that prevents the migration of moisture..
[Audio] Efflorescence is a common occurrence on stone masonry. It is characterised by a white crystalline substance which appears on the brick or stone's surface caused by the salts present in the construction materials or water used in the making process. This type of damage differs to rising dampness, as it occurs when a wall gets wet and then dries out; the dissolved salts come to the surface and draw water from the atmosphere, creating unsightly patches. To prevent this, the wall should be washed to remove all salt residue, and then repointed and sealed with a quality masonry sealer. Furthermore, the wall should be inspected for any visible signs of damage or deterioration and any necessary repairs should be made..
[Audio] To combat efflorescence on repairing stone masonry walls made with random rubble, measures must be taken to ensure construction materials such as bricks and sand do not contain salts. A damp-proof course should be installed at the plinth level to prevent the wall from getting moist, and rainwater should not be allowed to wet the wall. Repair begins by removing the plaster from the wall and scrubbing its surface with a brush to remove salts. Mildly hydrochloric acid should then be used to clean the surface entirely. After plastering and drying, the wall should not be exposed to further dampness..
[Audio] In this slide we are looking at the repair of random rubble masonry and RCC slab. Patch repair is required on the top surface of the slab and RCC slab with bottom steel corroded may necessitate special repair. Furthermore, any falling off of bottom plaster of the new RC slab may be due to an absence of proper bonding. To guarantee satisfactory repair of such surfaces, it is essential to recognise the precise cause of the damage and take the suitable steps to rectify it..
[Audio] Identify and mark out the perimeter lines for the repair with a line at least 100mm outside the worn area. Use a concrete saw to cut a groove of 3mm wide and 6mm deep into the surface. Remove any rust on the reinforcement bar and clean off before the repair area is cleaned by compressed air. Thoroughly wet the area and remove all the water. The area is then ready to accept the filling material..
[Audio] Stone masonry walls that are old can be repaired using random rubble and making 'through bond' connections between them. This is a common practice in modern stone masonry. In this slide, we will be discussing the repair of RCC slab with corroded bottom steel. Corrosion of steel and cracking of the bottom of older RCC roofs is usually caused due to leakage and seepage of water. If corrosion of slab bars occurs in other floor slabs, it is important to identify the cause, whether it be carbonation or chloride corrosion. If it is chloride corrosion, repair may need to be done again in the future..
[Audio] We will be discussing the repair of stone masonry, or random rubble masonry walls. This involves supporting the slab with props to take some of the load, then removing all defective concrete and exposing the corroded reinforcement to its full circumference. A clear gap of 15mm below the steel is recommended and a carbonation test may be conducted to find the depth of carbonation, with concrete removed up to this depth. The reinforcement should be cleaned thoroughly, and extra bars, if required, welded onto the old bars. Afterwards, a protective coating such as cement slurry or epoxy coating should be applied to the reinforcement. After this, a bonding coat should be applied on the surface of concrete, followed by the application of a polymer modified mortar, before the bonding coat dries. Finally, the surface should be cured for at least 7 days using water and painting with cement paint or carbonation resistant paint can be carried out after the surface has dried..
[Audio] When repairing stone masonry, it is important to create a 'Through Bond' in random rubble masonry walls and connections between existing stone walls. This ensures that the plaster at the bottom of a concrete slab does not fall off due to a lack of bonding. To achieve this, one can either use the traditional technique of hacking with a pointed tool so that the depression is at least 3mm deep and spaced no more than 50mm, or use modern construction chemicals for a smoother surface. Doing so ensures a strong bond between the slab and the masonry and is ultimately beneficial..
[Audio] I'm going to talk about the repair of stone masonry and the process of making ‘through bond’ in random rubble masonry, as well as the connection between existing stone walls. In addition, I’ll cover the strengthening of RCC slab with overlays and with underlays. The flexural performance of the slabs can be improved with overlays or underlays. The addition of these layers will also increase the stiffness and control the excessive deflection. Slabs with negative moment deficiency will be strengthened by an overlay, while those with positive moment deficiency will be strengthened by an underlay. Thank you very much for your attention..