Paddy Engineering Consultant

Cracking caused by plastic shrinkage in concrete occurs most commonly on the exposed surfaces of freshly placed floors and slabs or other elements with large surface areas when they are subjected to a very rapid loss of moisture caused by low humidity and wind or high temperature or both. Plastic shrinkage usually occurs prior to final finishing, before curing starts. When moisture evaporates from the surface of freshly placed concrete faster than it is placed by curing water, the surface concrete shrinks. Due to the restraint provided by the concrete on the drying surface layer, tensile stresses develop in the weak, stiffening plastic concrete, resulting in shallow cracks that are usually not short and run in all directions. In most cases, these cracks are wide at the surface. They range from a few millimeters to many meters in length and are spaced from a few centimeters to as much as 3 m apart. Preventing Plastic Shrinkage Cracks in Concrete Plastic shrinkage cracks may exte...

Factors that affects the concrete mix design strengths are: Variables in Mix Design A. Water/cement ratio B. Cement content C. Relative proportion of fine & coarse aggregates D. Use of admixtures A. Water/cement ratio Water to cement ratio (W/C ratio) is the single most important factor governing the strength and durability of concrete. Strength of concrete depends upon W/C ratio rather than the cement content. Abram’s law states that higher the water/cement ratio, lower is the strength of concrete. As a thumb rule every 1% increase in quantity of water added, reduces the strength of concrete by 5%. A water/cement ratio of only 0.38 is required for complete hydration of cement. (Although this is the theoretical limit, water cement ratio lower than 0.38 will also increase the strength, since all the cement that is added, does not hydrate) Water added for workability over and above this water/cement ratio of 0.38, evaporates leaving cavities in the concrete. These caviti...

Construction Materials management can be defined as "the function responsible for the coordination of planning, sourcing, purchasing, moving, storing and controlling materials in an optimum manner so as a pre-decided service can be provided at a minimum cost". By another definition, "materials management can be said to be that process of management which coordinates, supervises and executes the tasks associated with the flow of materials to, through, and out of an organization in an integrated fashion". Lee and Dobler define materials management as, "a confederacy of traditional materials activities bound by common idea – the idea of an integrated management approach to planning, acquisition, conversion, flow and distribution of production materials from the raw material state to the finished product state." From the above definitions, it is clear that the scope of materials management is vast. It has, directly or indirectly, impact on the activities ...

Repair of small, medium and large cracks in concrete and repair of crushed concrete is required to enhance the strength and durability of damaged concrete members. Repair of small and medium cracks in concrete: Small and medium cracks in reinforced concrete and masonry structures reduce their strength considerably to bear the design loads. Thus repair of such cracks is necessary to restore the designed strength of members. The repair of small and medium cracks is done by first marking out the critical damaged zones in concrete members. Then these cracks can be repaired by injecting cement grout or chemical grouts or by providing jacketing. The smaller cracks less than 0.75 mm width can be effectively repair by using pressure injection of epoxy. The surface of the member near cracks is thoroughly cleaned. Loose materials are removed and plastic injection ports are placed along the length of crack at an interval equal to the thickness of the structural member. These ports are pl...

Type of work App. Concrete Mix Max. size of aggregates (mm) Water for one cement bag batch (ltr) Total for dry aggregates For aggregates condition from dry to moist Best consistency Small precast work, fence posts, poles, garden furniture and other work of very thin sections 1:2:2 16 20 15 to 16 Soft Storage tanks, cisterns, sewers, well knerbs, watertight work, and columns or other structural parts subjected to high stresses 1:2:3 20 25 19 to 22 Medium Reinforced concrete work, floor slab, beams, columns, arches, stairs etc 1:2.5:3.5 20 32 23 to 27 Medium or soft Ordinary floors, footpaths, drive ways, steps, roads, pavements 1:2.5:3.5 20 23 20 to 23 Stiff Building and basemenot walls, silos, sills, lintels, machine foundations subject to vibration, Bridges, dams, piers, etc exposed to action of water and frost foundation concrete for masonry walls 1:2:4 40 30 23 to 26 Stiff or Medium Culverts, retaining walls, compound walls, ordinary machine bases, etc. 1:3:5 40 34 26 to 30...

Project managers are accountable for the success of a project. They will use their knowledge, skills and tools to ensure that the project requirements are met and that the project is meeting the set goals in a timely manner. The project manager is responsible for planning; executing and closing the projects which means they define the project then build a work plan and manage the budget through the end. They will also manage the teams associated with the project. HERE are step by step procedures to become a project manager. College Education: A college education is essential for obtaining a job as a project manager. The higher the education, the more likely the person will be chosen to be a project lead. A minimum of a Bachelor’s of Science degree in Project Management is generally required to be considered for a project. Project managers may elect to continue their education and obtain a Master’s of Science degree and even a Doctoral degree in project management. Once the degree i...

In this article, i will discuss on how building construction process actually works in the real world. So many construction projects are seen around us under different construction companies and contractors. The construction work that we see around us are only a part of the total procedure. The step by step work involved in building construction process is discussed in brief. Steps of Building Construction Process Building construction is a systemic work by work process. The followings are the steps of construction process. Preliminary Investigation Preliminary investigation will be made and preliminary estimate will be prepared together with sketch plans by a construction professional like those at Armstrong Steel. Administrative Approval Administrative approval of the department concerned will then be obtained. Land Acquisition At this stage of building construction process, land acquisition proceeding will be started. Detailed Survey Detailed survey will be made...

Following are the materials which are used for formwork: Plywood: This is by far the most common material used for the facing panel. It is easily cut to shape on site, and if handled and stored carefully, it can be used many times. Note the different thickness: A standard plywood thickness on site is 18mm. this is usually sufficient for most pours. However, if the formwork is curved, a thinner plywood is used to facilitate bending. Thicker plywood may be used when the weight of concrete causes a standard thickness plywood to bow out, distorting the concrete face. Timber: This is the most common material used for bracing members to the form face. Like plywood, it can be easily cut to size on site. Formwork made from timber is called traditional formwork. The construction methods using timer formwork have been used on site for years, and all well understood by trained operators. Steel: Steel is also used in pre-fabricated formwork. Purpose made steel forms are fabricated...

Designing and building formwork effectively requires a basic understanding of how concrete behaves as it exerts pressure on formwork. Concrete exerts lateral pressure on the formwork. The formwork is designed based on these lateral forces. Lateral concrete pressure on formwork is affected by: 1) Height of concrete pour 2) Concrete pour rate 3) Weight of concrete 4) Temperature 5) Type of cement 6) Vibration 7) Concrete slump (water–cement ratio) 8) Chemical additives 1) Height of concrete pour: Before concrete hardens, it acts like a liquid and pushes against the forms the way water presses against the walls of a storage tank. The amount of pressure at any point on the form is directly determined by the height and weight of concrete above it. Pressure is not affected by the thickness of the wall. Lateral concrete pressure on formwork 2) Concrete pour rate: Concrete pressure at any point on the form is directly proportional to the height of liquid concrete above it....

Formwork is a temporary mould into which fresh concrete and reinforcement are placed to form a particular reinforced concrete element. A typical breakdown of total construction percentage costs shows that formwork material and labour alone consists of 35% of the total concrete construction cost. In the construction of a structural element, the cost distribution can be found approximately as: . Concrete Cost – Materials 28%; Labour 12% = 40% . Reinforcement Steel Cost -Materials 18%; Labour 7% = 25% . Formwork Cost – Materials 15%; Labour 20% = 35%. To ensure that the formwork is economical and practical to build, the following basic technical, economical and functional requirements that should be kept in mind when designing and constructing formwork. Technical requirements of formwork: . Formwork should be of the desired shape, size and and fit at the location of the member in structure according to the drawings. . Formwork shall be carefully selected for required f...

Mortar and Concrete Mortar is a mixture of sand and cement that is usually used to build bricks or blocks. Concrete on the other hand has a composition of broken stone, sand, cement and water. This article concentrates on the basic differences in between mortar vs concrete. Differences between mortar vs concrete There are many who are confused on the differences between cement, mortar and concrete. Previously, we discussed the dissimilarities of cement and concrete. Now let’s discuss about the differences between mortar and concrete. Mortar Concrete Thick mixture of sand and cement (its composing elements). Mixture of sand and cement and water but also chippings of stones and rocks. It is less durable than concrete. Because of its composing elements it is much stronger as compared to the former. The water to cement ratio is higher in mortar and hence acts as perfect glue to bonding materials like brick. Low  water to cement ratio  making i...

A safe practice for formwork during construction at site is important for safety of workmen. Improper erection of formwork can cause damage to structural element as well as pose threat to the safety of workmen. Following are the safe practices checklist for formwork: Formwork Safety Checklist during Design: 1. Formwork should be properly designed for the structural element considered and its working drawing should be available at site. 2. Design of formwork should consider all the loads it will experience during casting of concrete structural members. 3. Strength of materials used for formwork should be adequate to support structural load as well as other loads imposed on it. 4. Formwork design should indicate the rate of concrete pour, height of concrete pour, temperature and sequence and schedule of concrete pours. 5. Working drawing of formwork should have detailed dimensions including pouring pocket size, compaction opening and cleanouts. 6. Formwork design should consi...

Metal roof Metal roofs and shingle roofs are different. Metal roof is simply a roof made of metal and tends to have very high purchase and installation costs. It is great for keeping a house cool during the summer. Also it is often the most environmentally-friendly roofing option. Shingle roof Shingle roofs are often cheaper to buy and install than other types of roofing. It can be environmentally-friendly in some cases. The problem is that shingle roofs are not able to last as long as metal roofs. It needs more maintenance than metal roofs. Metal roof vs Shingle roof – What’s the difference The pros and cons of each type of roof can be a stark contrast in some cases. For example, a metal roof is great during the summer and a shingle one is great during the winter. The differences between metal roofs and shingle roofs are listed in the below  metal vs shingle roof  table. Metal Roof Shingle Roof With good and proper insulation, you can achieve fairly good soun...

Flat roofs and sloped roofs both are used frequently in modern constructions. Before choosing flat or sloped roof, you should know the advantages and disadvantages of both the roofs. Advantages of flat roofs than sloped roofs Here are some of the advantages of using flat roofs than sloped roofs listed below: 1. The construction process for flat roofs are simple. 2. For playing, gardenning, sleeping etc flat roofs are very effective. 3. Flat roofs can be made fire resistant more easily than the sloped roofs. 4. It has good insualtion than sloped roofs. 5. The total area required for roofing materials are lesser when flat roofs are used. The area is greater for sloped roofs. 6. Sloped roofs require ceiling while flat roofs don’t. 7. Flat roofs are more fire resistant. 8. Flat roofs are more stable while resisting wind pressure. Flat Roof Sloped Roof Disadvantages of flat roofs than sloped roofs Flat roofs are not always advantageous. Flat roofs has also m...

Hardwood Floor on Concrete Slab Hardwood floors look very impressive. There are many of us who want to change the look of our house floors by installing hardwood floor on the regular concrete slabs. It is possible to do so, but this process is complex. However, once you finish doing it you will like it, which is guaranteed. Before you commence installing hardwood slab on your concrete floor, remember to consider a few things. These involve flatness and moisture. Before installing the hardwood slab you must check the whole concrete surface is built and ensure that it lies flat within a 3/16’’ in a measured 10 foot range radius or within a 1/8’’ in a measured 6 foot range radius. You can do this by taking a 6 foot or 10 straight foot edge and placing it in various places on the sub floor. This will enable you to notice the dips very clearly. If you notice just a couple of dips, then you can take mortar (non-shrinking) and fill the dips. There are many repair products available in the ...

Post Tension Slab Although concrete is a strong material for construction, it is not resistant to breakdown especially where longer concrete slabs are required like in a bridge or a length of a beam. For this, the concrete slab is tensioned with a process called pre-stressing and the slab of concrete which comes out after this process is known as post tension slab. This slab is much stronger as well as more durable than the normal concrete slabs. In today’s world, where the modern engineering is finding new ways to build longer, more efficient and stronger structures, post tension slab becomes one of their chief requirements. There are many advantages and disadvantages of post tensioned slabs which we will discuss in this post. Advantages of Post Tension Slab Post tension slabs are advantageous in many ways. Some of the major benefits of post tension slabs are as follows. 1. Reduced cost: Post tension slabs are excellent ways to construct stronger structures at an affordable...

What is a floating slab? These slabs are constructed in two stages. In the first stage the footings are poured separately. The center floor of the floating slab is poured only after the footings have been cured. The slab is not anchored to the floor. This type of slab is typically used for shallow foundations like garages, sheds and light home extensions. Floating slab construction A building construction typically needs a solid foundation in which it can bear the weight of the entire structure, including the roof, floor and other loads it may contain. However, small structures such as sheds, garages, backyard extensions do not need elaborate and extra strong foundations as they are generally light in structure. Floating slab is an ideal solution for such basic foundation structures. This type of slab foundation is mostly used in northern climates as the slab does not require concrete footing with deep extensions below frost line. Floating slab is sometimes known as a raft foun...

Defects in plaster Plaster can be cracked or damaged due to the following causes: 1. If the proportion of sand in plaster is excessive or low quality sand is used then the plaster can be cracked. 2. If plaster is dried out because of improper curing then it can be cracked. 3. Plaster should be placed properly with the background, otherwise it will get defected and fall apart slowly. 4. After applying first layer it should be given the time to dry out before applying the second layer. Otherwise, hair crack may appear in the plaster later. How to rectify defects of plaster The defects of plaster can be rectified by following the below steps: 1. Before plastering, water should be applied to the surface to make it wet so that the surface won’t suck water from the plaster. 2. Don’t rub too much trying to make the surface smoother. 3. Use good bricks in masonry works. 4. Salt free water should be used in construction works. 5. Efflorescence can be reduced by brush...

Asbestos is one of the oldest materials used in industrial applications. Asbestos in Plaster is merely one of the recent methods of using it. Asbestos fibers have high strength while being 100-200 times thinner when compared with a strand of human hair. Its application is due to its most significant property of all – heat insulation. Use of asbestos has become quite limited these days in the 1st world countries. Though for its high end insulation properties, asbestos in plaster has often been used in various development projects. Types of Asbestos in Plaster In a general sense, there are two types of Asbestos in Plaster namely, loosely bound fibers and firmly bound fibers. Loosely bound fibers contain strands of asbestos loosely bound. These do not provide greater structural integrity or strength and are used to insulate stoves and heaters. Ever since asbestos has been banned, glass fibers are slowly taking their place. Firmly bound Asbestos in Plaster offer structural support a...

Lath and Plaster is one of the most preferred ways of finishing the internal surface of one’s home. It was a common method used in the 1950s, consisting of sawing or riveting thin strips of wood (laths). These strips are covered with plaster and leveled off. Just as with other things, they also require minor repairs to last for their expected years. Cost effective methods Short Term: Repairing Lath and Plaster in your home requires key decisions in the areas of time, budget and the final appearance required. The first choice is to remove dust by vacuuming and simply re-decorating with any suitable paint (preferably water based). However, this method is the best before the plaster starts to sag and crack. The cost is low and depends on the original condition of the plasterwork. Though this is best for cottages and buildings that exude an old-world charm, it is a short term solution and cannot give a ‘flat’ finish. The next method is to scrape out the cracks and remove the loo...