MAIN CAMPUS San Roque, Sogod, Southern Leyte Email: president@southernleytestateu.edu.ph Website: www.southernleytestateu.edu.ph Excellence | Service | Leadership and Good Governance | Innovation | Social Responsibility | Integrity | Professionalism | Spirituality CONTRACTION AND CONSTRUCTION JOINTS CONTRACTION JOINT The purpose of weak joints in concrete is to create a predetermined location for cracking to occur at regular intervals. These joints produce square panels that should not exceed a length to width ratio of 1 ½ to 1. They are commonly spaced at distances equal to 24 to 30 times the slab thickness and are known as control joints or contraction joints. There are three methods for creating contraction joints when working with concrete. The first involves inserting a premolded strip into the concrete while it is being placed, which will create a weakened plane. Alternatively, metal or plastic strips can be added to concrete pavements to prevent cracks. The second method involves saw cutting or dry cutting joints into the concrete after it has been placed. Saw-cut joints should be made within 4 to 12 hours of finishing, while dry-cut joints should be made 1 to 4 hours after finishing. A permeable material is inserted into the joints to bond with the concrete. The third method involves forming a sawn joint once the concrete has sufficiently hardened. This should be done as early as possible to avoid unplanned cracking, and the joint should be filled with sealant to prevent debris from entering. Location of Contraction Joints Contraction joints form a convenient point at which to stop concrete work at the end of the day. Construction joints should never be formed in the middle of a bay. Hence, contraction joint is placed at the location of highest concentration of tensile stresses resulting from shrinkage are expected: At abrupt changes of cross-section; and FOLLOW US HERE: https://www.facebook.com/southernleytestateu/ https://www.youtube.com/c/SouthernLeyteStateUniversity MAIN CAMPUS San Roque, Sogod, Southern Leyte Email: president@southernleytestateu.edu.ph Website: www.southernleytestateu.edu.ph Excellence | Service | Leadership and Good Governance | Innovation | Social Responsibility | Integrity | Professionalism | Spirituality In long walls, slabs. CONSTRUCTION JOINTS When concrete is placed at different times, a joint between slabs is created, which is known as a construction joint. These joints can be classified as transverse or longitudinal construction joints. Longitudinal joints permit slab warping without causing any significant separation or cracking of the slabs. Construction joints are typically placed at areas where two successive concrete placements occur, usually at the end of a day's work or when concrete placement is halted for longer than the initial setting time of concrete. They can be designed for slab movement and/or load transfer, and their locations should be predetermined. Construction joint can be of two different types. Butt Joints: A butt joint is the most basic kind of construction joint and is created by using a regular bulkhead board. For thin slabs, use this joint. FOLLOW US HERE: https://www.facebook.com/southernleytestateu/ https://www.youtube.com/c/SouthernLeyteStateUniversity MAIN CAMPUS San Roque, Sogod, Southern Leyte Email: president@southernleytestateu.edu.ph Website: www.southernleytestateu.edu.ph Excellence | Service | Leadership and Good Governance | Innovation | Social Responsibility | Integrity | Professionalism | Spirituality Tongue and Groove Joints: A joint that resembles tongue and groove lumber construction can be used in slabs. The keyway may be created by attaching pre-molded key material to a wood bulkhead, or by joining metal, wood, or both. It is best to hand-tool or save the concrete above the joint so that it resembles a control joint. Construction joints are necessary in most reinforced concrete construction. Due to their critical nature, they should be located by the designer, and indicated on the design drawings to insure adequate force transfer and aesthetic acceptability at the joint. If concrete placement is stopped involuntarily for a time longer than the initial setting time of the concrete, the joint should be treated as a construction joint, with advance input from the designer as to any additional requirements needed to insure the structural integrity of the element being placed. FOLLOW US HERE: https://www.facebook.com/southernleytestateu/ https://www.youtube.com/c/SouthernLeyteStateUniversity MAIN CAMPUS San Roque, Sogod, Southern Leyte Email: president@southernleytestateu.edu.ph Website: www.southernleytestateu.edu.ph Excellence | Service | Leadership and Good Governance | Innovation | Social Responsibility | Integrity | Professionalism | Spirituality ADMIXTURES CHEMICAL ADMIXTURES Chemical admixtures are substances added to concrete during mixing to modify its properties and improve construction efficiency. They can reduce costs, enhance the quality of concrete, and address specific challenges. Admixtures are added either at the plant or on-site, with some specialty admixtures being manually batched. Their effectiveness depends on factors such as cement type, water content, mixing time, slump, and temperatures. There are five main classes of chemical admixtures: air-entraining, water-reducing, retarding, accelerating, and plasticizers (superplasticizers). Air-entraining admixtures create microscopic air bubbles in concrete, while water-reducing admixtures decrease water content and improve strength without increasing cement amount. Retarding admixtures slow down concrete setting, useful in hot weather, while accelerating admixtures speed up early strength development, curing, and finishing, particularly in cold weather. Superplasticizers reduce water content, creating highly fluid and workable concrete. Specialty admixtures serve specific purposes such as corrosion inhibition, shrinkage reduction, alkali-silica reactivity reduction, workability enhancement, bonding, damp proofing, and coloring. Corrosion inhibitors protect reinforcing steel from corrosion, shrinkage reducers control drying shrinkage and cracking, and alkali-silica reactivity inhibitors address durability issues related to certain aggregates. FOLLOW US HERE: https://www.facebook.com/southernleytestateu/ https://www.youtube.com/c/SouthernLeyteStateUniversity MAIN CAMPUS San Roque, Sogod, Southern Leyte Email: president@southernleytestateu.edu.ph Website: www.southernleytestateu.edu.ph Excellence | Service | Leadership and Good Governance | Innovation | Social Responsibility | Integrity | Professionalism | Spirituality MINERAL ADMIXTURES Mineral admixtures are substances that are added to concrete in the form of fine powders or particles. These admixtures are typically obtained from industrial by-products or natural materials and are used to enhance the properties of concrete. Here are some common types of mineral admixtures: Fly Ash: Fly ash is a by-product of coal combustion in power plants. It consists of fine particles that can be used as a partial replacement for Portland cement in concrete. Fly ash improves workability, reduces heat generation, enhances long-term strength and durability, and reduces the permeability of concrete. Silica Fume: Silica fume is a by-product of the production of silicon metals and alloys. It is a very fine pozzolanic material that reacts with calcium hydroxide in the presence of water to form additional cementitious compounds. Silica fume improves concrete strength, reduces permeability, enhances durability, and mitigates the effects of alkali-silica reaction. Ground Granulated Blast Furnace Slag (GGBFS): GGBFS is a by-product of the iron and steel industry obtained by quenching molten blast furnace slag in water or steam. It is a cementitious material that can be used as a partial replacement for Portland cement. GGBFS improves workability, reduces heat of hydration, increases long-term strength, enhances durability, and reduces the risk of sulfate attack. Natural Pozzolans: Natural pozzolans such as volcanic ash, calcined clay, and diatomaceous earth are finely divided materials that react with calcium hydroxide in the presence of water to form cementitious compounds. Natural pozzolans can improve workability, reduce permeability, enhance long-term strength, and provide resistance to sulfate attack. Mineral admixtures provide numerous benefits in the production of concrete. They enhance the strength and longevity of concrete, decrease the need for cement, lower heat generation during the curing process, and promote sustainable construction by utilizing industrial by-products. However, it is crucial to carefully assess the unique properties of each mineral admixture and adjust the concrete mixture accordingly to attain the desired outcomes. FOLLOW US HERE: https://www.facebook.com/southernleytestateu/ https://www.youtube.com/c/SouthernLeyteStateUniversity MAIN CAMPUS San Roque, Sogod, Southern Leyte Email: president@southernleytestateu.edu.ph Website: www.southernleytestateu.edu.ph Excellence | Service | Leadership and Good Governance | Innovation | Social Responsibility | Integrity | Professionalism | Spirituality Assignment No. 1 CONSTRUCTION MATERIALS AND TESTING (LEC) [ Contraction Joints and Construction Joints; Admixtures ] Submitted by: RODEL E. ELICOT BSCE - 2A Submitted to: DR. ANACLETA L. DAGAAS Instructor FOLLOW US HERE: https://www.facebook.com/southernleytestateu/ https://www.youtube.com/c/SouthernLeyteStateUniversity
