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Tips_and_tricks
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Why is the characteristic compressive strength fck reduced to 0.67 fck?

  1. Kuldeep Singh

    Kuldeep Singh

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    Kuldeep Singh Learner

    I agree with the reason given by CB Sowmya, but only partially. We don't assume concrete strength to be 2/3rd of the characteristic strength, but there's a logical reason behind it. She's only stated the shape factor with the correct 20% decrease in strength, but there is also a size factor. What haRead more

    I agree with the reason given by CB Sowmya, but only partially.

    We don’t assume concrete strength to be 2/3rd of the characteristic strength, but there’s a logical reason behind it. She’s only stated the shape factor with the correct 20% decrease in strength, but there is also a size factor.

    What happens is, first of all, due to slenderness, concrete cylinders have shown to have 80% of the characteristic strength corresponding to 150mm cubes. But also, even concrete cubes of sizes exceeding 450mm show only 85% the strength as compared to the standard 150mm ones. Since the concrete members will neither be cubes and not just 450mm, we need to take into account both the factors.

    So, the new compressive strength becomes 0.8*0.85*fck = 0.68 fck. Now, 0.68 fck is very close to 0.67 fck or fck/1.5. So, for a rounder figure, we take it as 0.67 fck.

    Note: This 1.5 isn’t the factor of safety. (FoS). A factor of 1.5 is further applied for design and the design strength becomes 0.67 fck / 1.5 = 0.446 fck.

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dhiraj010kumar
dhiraj010kumar

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While preparing a Design Mix for any Grade, if we have aggregated in two sizes like 10 mm & 20 mm or In fact Sometimes, we do use to have 40 mm aggregate as well. Is there Any IS Code Provision ...

  1. dbnalawade

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    Following points part of the answer to the question : IS 456  and IS 1343 are the code of practice you can use. The method of proportions aggregates for concrete is part design mix process. Size and Grading impacts the design mix greatly. larger the size of aggregate smaller is the cement requiremenRead more

    Following points part of the answer to the question :

    • IS 456  and IS 1343 are the code of practice you can use.
    • The method of proportions aggregates for concrete is part design mix process.
    • Size and Grading impacts the design mix greatly.
    • larger the size of aggregate smaller is the cement requirement for a given W/C ratio
    • Compressive strength of the mix tends to increase with decrease in aggregate size.
    • perform gradation tests using sieves. Coarse aggregates should conform to table 2 of IS 383 and Fine aggregate should conform to Zone 1 of IS 383

    There is ACI method available for the same exercise ACI 211.1is the code you can use.

     

    Hope this helps.

     

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krishna
krishna

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Rate analysis for block size 30cmx20cmx15cm with mortar ratio of 1:2:4 including labour cost

  1. Komal Bhandakkar

    Komal Bhandakkar

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    This answer was edited.

    Rate analysis: Rate analysis will simply the quantity of cement and sand required for the 1-meter cube of cement sand mortar. Similarly, we can do rate analysis for concrete as well for different proportions. Here I am discussing point example of the material required for the 1-meter cube of cementRead more

    Rate analysis:

    Rate analysis will simply the quantity of cement and sand required for the 1-meter cube of cement sand mortar.

    Similarly, we can do rate analysis for concrete as well for different proportions.

    Here I am discussing point example of the material required for the 1-meter cube of cement concrete of density 2.3 ton per metre cube and cement sand aggregate ratio is 1:3: 6

    Mix proportion ratio is 1:3:6 (here, maximum 20 nominal sizes of aggregates are used.)

    The total sum is 1+ 3 + 6=10 Dry volume of 1-metre cube concrete is a 1.54-metre cube.

    Hence cement required is a one-tenth part of the 1.54-meter cube which is 0.15-metre cube means to 16 kg means 4.3 bags of 50 kg each.

    If you want to find out the sand quantity then it’s 0.46-meter cube means 1.2-ton Aggregate quantity 0.92-metre cube means 1.56 ton of maximum normal size of 20 mm aggregate

    I hope so your doubt is clear, thank you.

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Jam
Jam

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Hi, Fellow engineers and builders!! What could be the possible pros and cons of using beach sand instead of river sand in concrete mix for structural members (i.e. Substructures to Superstructures) on a vicinity where beach sand is predominant than river ...

  1. dbnalawade

    dbnalawade

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    Only good thing about beach sand is that it is available in plenty. Beach sand is laden with salts, chloride and sulphates are very harmful elements leading to deterioration of reinforcement and concrete. This calls for cleaning the sand incurring huge costs. In Middle East sand is mined and washedRead more

    Only good thing about beach sand is that it is available in plenty.

    Beach sand is laden with salts, chloride and sulphates are very harmful elements leading to deterioration of reinforcement and concrete. This calls for cleaning the sand incurring huge costs. In Middle East sand is mined and washed several times to get rid of the salt.

    Physical properties of the beach sand like fitness modulus and shape criteria  may not help  produce workable concrete.

     

     

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Komal Bhandakkar
Komal Bhandakkar

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Sugar is act as an accelerator or retarder in concrete?

  1. Preet Chovatiya

    Preet Chovatiya

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    Sugar meddles with the concrete restricting cycle in the solid. Note that solid and concrete are not equivalent. Concrete is made by consolidating concrete, water and a filler material called a "total," like rock or sand. Most concrete is produced using limestone and dirt. It responds with water toRead more

    Sugar meddles with the concrete restricting cycle in the solid. Note that solid and concrete are not equivalent. Concrete is made by consolidating concrete, water and a filler material called a “total,” like rock or sand. Most concrete is produced using limestone and dirt. It responds with water to frame a solidifying glue that ties the total together to create hard concrete. This solidifying cycle is called hydration.

    One hypothesis recommends that when the solid combination contains sugar, the sugar particles connect themselves to the hydrating solidify and repress the synthetic responses associated with hardening the material.

    sugar builds the centralizations of calcium, aluminum, and iron in concrete. The sugar particles consolidate with these metals to frame insoluble compound buildings that coat the concrete grains. A few key synthetic cycles that solidify the solid are then hindered. Hydration hinders the cycle and the solid takes more time to set. Thus, sugar is known as a retarder. Retarders increment the setting season of cement.

    Refined white sugar is extraordinary compared to other retarders. Lactose, the sugar found in milk, is a moderate retarder. Trehalose, a sugar created by different parasites, is non-hindering and doesn’t influence setting time.

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vivek gami
vivek gami

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We all know about slag cement, but what is slag which is used in cement? How slag affect cement property?

  1. Nimesh Gajera

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    Nimesh Gajera Learner

    Slag is actually a by-product of the smelting process to obtain metal from raw ore. Slag cement is made by grounding blast furnace slag to proper fineness and used as a replacement of portland cement. Slag has some cementitious properties itself. Slag cement gives some extra strength, enhance resistRead more

    Slag is actually a by-product of the smelting process to obtain metal from raw ore. Slag cement is made by grounding blast furnace slag to proper fineness and used as a replacement of portland cement. Slag has some cementitious properties itself. Slag cement gives some extra strength, enhance resistance to chemical attack, reduce permeability, protect rebar from corrosion. And it has some disadvantages like it reduces the initial setting time of cement.

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Gopal Mishra
Gopal Mishra

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I am doing a project on “Hybrid reinforced concrete with steel  and banana fibres. What should be the procedure to carry out this project? Please guide me.

  1. Gopal Mishra

    Gopal Mishra

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    Gopal Mishra

    Reinforced concrete construction requires compressive strength and certain properties such as workability and durability. When adding banana fibers with concrete, I have no idea what property of concrete you are trying to modify. Can you share more details about your project on what are your thoughtRead more

    Reinforced concrete construction requires compressive strength and certain properties such as workability and durability. When adding banana fibers with concrete, I have no idea what property of concrete you are trying to modify. Can you share more details about your project on what are your thoughts while selecting this topic? Which property of concrete will it affect?

    For your project topic, you can divide your research in two parts:

    1. Effect on fresh concrete
    2. Effect on hardened concrete.

    Effect on fresh concrete

    The most important effect on fresh concrete will be its workability. While adding banana fibers in concrete, please check for its effect on workability at various proportions of banana fibers with cement at a constant water content.

    Then change the water content and retry tests for workability at different banana fibers content.

    Based on the result, you can select the optimum water content and banana fibers.

    Effect on hardened concrete

    Effect on hardened concrete is its compressive strength at 28 days. For various proportions of banana fibers and water cement ratio, you must evaluate its effect on concrete compressive strength. These tests must be carried out for various water content ratio and banana fiber contents.

    A study must also be conducted for what will be the life of banana fibers inside concrete? Will it decay? What happens when it decays?

    Based on your feedback about what is your actual goal, I can provide other guidelines.

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Leon
Leon

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I purchased a home and with all the recent rain I removed the basement paneling to find a leak. I discovered the home at one time had no garage. T some time the window well (see attachment) had been covered ...

  1. AdityaBhandakkar

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    Below grade window fill

    Hi, Recently I go through the image you attached, yes it possible to repair the leakages and seal with concrete with some admixtures. I suggest you contact with the locally available contractor for repairs. But if you are a civil engineer, the following are some suggestions. Following are some repaiRead more

    Hi,

    Recently I go through the image you attached, yes it possible to repair the leakages and seal with concrete with some admixtures. I suggest you contact with the locally available contractor for repairs. But if you are a civil engineer, the following are some suggestions.

    Following are some repairing methods for leakages

    1. Resin injection: used for repairing the concrete saw delaminated and also used for joints that experience water leakage. Metals are used for rebound cracks, whereas polyurethanes and acrylic acrylates are used to seal the cracks and joints that leak water.
    2. Stitching cracks: it is a long-lasting and easiest method where the holes are drilled, and the surface is stitched with the help of a metallic wire. Is metallic wires are passed through the holes and anchored strongly, and the vacant spaces are grouted.
    3. Gravity field method: in this method instrument with waterproofing admixture used to fill the cracks with the help of the gravity where it is allowed to move inside the cracks by gravity forces and sealed it. It is used for the cracks with width 0.03mm to 20mm cracks
    4. Micro toppings: Polymer with 1/8 inches, which contained a modified concrete and sand, are applied with the help of trowels. This treated surfaces can be allowed for public use within 36 to 42 hours of usages.
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