concrete tech

  column:  When  vertical load carry and slab and beam dead load and live load transfer to footing that is called column .  Column may be classified into the following two types, depending on whether slendeness effects   are considered insignificant or significant  1.        Short column 2.          Long column        The road of effective column length to least lateral dimension is referred to as ‘slenderness ratio’ Columns with slenderness ratio between 3 to 12 are short column which invariably fail under ultimate loads with the material reaching its ultimate strength and not by buckling Column with slenderness ratio between 12 to 60 are long columns . Column having slenderness ratio less than 3 are called as pedestal . Maximum longitudinal reinforcement in an axially loaded column is 6% of gross cross sectional area and minimum is 0.8% of gross cross sectional area. Columns with circular sections are mostly provided with transverse helical reinforcement, although th

       The elongation index of aggregate the percentage by weight particles  who's greatest dimension length is greater then 1.8 times there means dimension.  The flakiness index of the aggregate percentage by weight of particle whose dimension (thickness) is 0.6 times there men dimension           Sieve size(mm) Weight of aggregate taken in gram    (A) Weight of aggregate retained on thickness gauge in gram                (B) Weight of aggregate passing on thickness gauge in gram              (C) Weight of aggregate retained on length gauge in gram            (D) Passing     Retained 25mm 20mm 348 324 24 32 20mm 16mm 870 781 89 15 16mm 12.5mm 767 672 95 255 12.5mm 10mm 325 221

                                                      Testing Of Tiles Different types of test performed on tiles are as follows: a)       Transverse strength test: It consists of applying the load along the center line a right angle to the length of the tile (which has been immersed in water for twenty-four hours) supported on the rounded edges of wood bearers. Six tiles are tested and the average breaking load should not be less than specified.   Flexural strength (N/mm 2 )    =15WS/bt 2     Where W= breaking load, S= span in mm (3/4 of tile length), and b,               t= width and thickness, respectively. b)       Water absorption test (IS:2690): Six tiles are dried in oven at 105+_5 0 C and cooled at the room temperature. They are then immersed in water for twenty-four hours. Thereafter these are wiped dry and weighted.   Absorption in %=w 2 -w 1 /w 1 x100       Where, w 1 and w 2 are the respective weights of dry

Concrete shrinkage ·          The volumetric change of concrete structures due to the loss of capillary water by evaporation is known as concrete shrinkage or shrinkage of concrete. ·          It is a time dependent phenomenon which reduces the volumes of concrete without the impact of external forces. Types of shrinkage 1.        Plastic shrinkage: plastic shrinkage occurs very soon after curing the concrete in the forms. The hydration of cement results in reduction to the volumes of concrete. Due to evaporation from the surface of concrete, which leads to cracking. 2.        Drying shrinkage: The shrinkage that appears after the setting and hardening of the concrete mixture due to loss of capillary water is known as drying shrinkage. Drying shrinkage generally occurs in the first few months and decreases with time. 3.        Carbonation shrinkage: Carbonation shrinkage occurs due to the reaction of carbon dioxide (CO 2 ) with hydrated cement minerals, carbonating Ca (

  Ordinary Concrete Grade Ordinary grade concrete is not used for M40 & M25, as it includes only M10, M15 and M20. As per  IS 456:2000                                         Type of   Grades concrete               Group            Grade           Designation Specified characteristic compressive strength of 150mm cube At 28 days (N/mm 2 )      1 2 3 Ordinary concrete M10 M15 M20 10 15 20 Standard concrete M25 M30 M35 M40 M45 M50 M55 M60 25 30 35 40 45 50 55 60 High strength concrete M65 M70 M75 M80 M85 M90 M95 M100 65 70 75 80 85 90 95 100                In the designation of concrete mix M refers to the mix & the number specifies characteristic compressive strength of 150mm size cube at 28 days, expressed in N