Showing posts from December 24, 2017


MAKING OF TEST CUBES FROM FRESH CONCRETE IS-456 has laid down the acceptance criteria of quality concrete. In all the cases, the 28-days compressive strength shall alone be the criterion for acceptance or rejection of the concrete. 7 days compressive strength of concrete can be carried out in order to get a relatively quicker idea regarding the quality of concrete. PROCEDURE OF TEST CUBE PREPARATION EQUIPMENT The following equipments are needed for the preparation of concrete cubes. Sample tray; Mould for making test cube; Spanner; Scoop; Steel float or trowel; Compacting bar; Cleaning rags; A bucket or barrow for transporting the samples; Curing tank Permanent Marker. NO OF CUBES 6 no of Cubes of 150 x 150 x 150 mm size shall be cast, 3 for 7-days testing and 3 for 28-days testing. A sample consists of 3 cube specimens and their average compressive strength represents the test result of that sample. The individual variation of a set of 3 cubes should not


COMPOUNDS OF CEMENT cement compounds About 90-95% of a Portland cement is comprised of the four main cement minerals, which are  C 3 S ,  C 2 S ,  C 3 A , and  C 4 AF , with the remainder consisting of calcium sulphate, alkali sulphates, unreacted (free) CaO, MgO, and other minor constituents left over from the clinkering and grinding steps. The four cement minerals play very different roles in the hydration process that converts the dry cement into hardened cement paste.  The C 3 S and the C 2 S contribute virtually all of the beneficial properties by generating the main hydration product, C-S-H gel.  However, the  C 3 S hydrates much more quickly than the C 2 S and thus is responsible for the early strength development .  The C 3 A and C 4 AF minerals also hydrate, but the products that are formed contribute little to the properties of the cement paste.  These minerals are present because pure calcium silicate cements would be virtually impossible to produce economicall


WHAT IS VOLUME BATCHING OF CONCRETE? Batching of concrete means measuring different ingredients of concrete (i.e. cement, sand, coarse aggregate and water) before mixing it. When this measurement is done on the basis of volume, we call it  Volume Batching . Below are mentioned some of important points to remember before adopting volume batching method in field. Volume batching is not a good method for measuring concrete materials. It is not applicable in case of reinforced concrete structure. This method of concrete batching may not be economical. It can be only used for unimportant concrete or for small concrete works. HOW VOLUME BATCHING IS DONE IN FIELD? Before batching concrete ingredients in terms of volume, we need to know two things. What is the relative proportion of concrete ingredients in terms of volume? What is the water-cement ratio? After knowing these two things you can proceed to batch concrete ingredients in field. The table shown below can be


FACTORS AFFECTING THE SETTING AND HARDENING OF PORTLAND CEMENT (1)  THE IMPACT OF CEMENT’S COMPOSITION The mineral composition of cement and their ratios are the main factors affecting the setting and hardening of cement. As mentioned above, various mineral components will reveal different characteristics when reacting with water. For example, the  increase of C3A  can  speed up the setting and hardening rate of cement , and the  heat of hydration is high  at the same time. Generally speaking, if mixed materials are added into the cement clinker, the anti-erosion will increase, and the heat of hydration and the early strength will decrease. (2)  THE MIXING AMOUNT OF GYPSUM Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in wate


HOW TO CLASSIFY SOIL SAMPLES BASED ON SAMPLING METHOD? NEED FOR SOIL SAMPLING A satisfactory design of a foundation depends upon the accuracy with which the various soil parameters required for the design are obtained. The accuracy of the soil parameters depends upon the accuracy with which representative soil samples are obtained from the field. Sampling is carried out in order that soil and rock description, and laboratory testing can be carried out. Laboratory tests typically consist of: Index tests (for example, specific gravity, water content) Classification tests (for example, Atterberg’s limit tests on clayey soil); and Tests to determine engineering design parameters (for example strength, compressibility, and permeability). FACTORS TO BE CONSIDERED WHILE SAMPLING SOIL i) Samples should be representative of the ground from which they are taken. ii) They should be large enough to contain representative particles sizes, fabric, and fissuring and fracturing.


HOW TO PLAN A SITE INVESTIGATION PROGRAM? SITE EXPLORATION PROGRAM The knowledge about the site forms a vital role in the safe and economical development of a site. A thorough investigation of the site is an essential preliminary to the construction of any civil engineering works. Public building officials may require soil data together with the recommendations of the geotechnical consultant prior to issuance of a building permit. Elimination of the site exploration, which usually ranges from about 0.5 to1 percent of total construction costs, only to find after construction has started that the foundation must be redesigned is certainly false economy. This is generally recognized, and it is doubtful if any major structures are currently designed without exploration being undertaken. OBJECTIVES OF SITE INVESTIGATION The primary objectives of soil exploration is mentioned below To access the general suitability of the site To achieve safe and economical design of foundatio


15 DIFFERENT TYPES OF LOADS ON BUILDING (IN SHORT) TYPES OF LOADS External loads on a structure may be classified in several different ways. In one classification, they may be considered as static or dynamic. Static loads  are forces that are applied slowly and then remain nearly constant. One example is the weight, or dead load, of a floor or roof system. Dynamic loads  vary with time. They include repeated and impact loads. Repeated loads  are forces that are applied a number of times, causing a variation in the magnitude, and sometimes also in the sense, of the internal forces. A good example is an off-balance motor. Impact loads  are forces that require a structure or its components to absorb energy in a short interval of time. An example is the dropping of a heavy weight on a floor slab, or the shock wave from an explosion striking the walls and roof of a building. External forces may also be classified as distributed and concentrated. Uniformly distributed loads  ar


PROPERTIES OF AGGREGATES FOR CONCRETE PROPERTIES OF AGGREGATES Approximately 75% of the volume of concrete is occupied by aggregates, so quality of aggregates plays an important role in determining properties of concrete.  Aggregates are chemically inert, solid bodies held together by the cement. Aggregates come in various shapes, sizes, and materials ranging from fine particles of sand to large, coarse rocks. Natural aggregates are formed by process of weathering and abrasion or by artificially crushing large parent mass. Because cement is the most expensive ingredient in making concrete, it is desirable to minimize the amount of cement used. 70 to 80% of the volume of concrete is aggregate in order to keep the cost of the concrete low. The selection of an aggregate is determined, in part, by the desired characteristics of the concrete. For example, the density of concrete is determined by the density of the aggregate. Soft, porous aggregates can result in weak concrete wi