9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? Questions (http://theconstructor.org/questions/) | Ask Question (http://theconstructor.org/add_question/) | Login Area Search here ... (http://theconstructor.org/) Go to... What is the grade of concrete(M20/M25 etc.) normally used in roof casting? How much PSC cement is required for making 1 cubic meter of concrete? Home (http://theconstructor.org) / Concrete (http://theconstructor.org/question-category/concrete/) / What is the grade of concrete(M20/M25 etc.) normally used in roof casting? How much PSC cement is required for making 1 cubic meter of concrete? http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 1/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? What is the grade of concrete(M20/M25 etc.) normally used in roof casting? How much PSC cement is required for making 1 cubic meter of concrete? Question I am building a small construction of about 700 square foot(picture attached). In roof casting my mason has used 60 bags of PSC cement though he estimated 74 bags before. I am in serious doubt what is going on. Could you please help me? Attachment (http://theconstructor.org/wpcontent/uploads/2016/06/13321797_1196003027096577_2269556106714869837_n.jpg) solved 5 Concrete (http://theconstructor.org/question-category/concrete/) Pal Chakraborty (http://theconstructor.org/pro䕕ሥle/pal 3 months chakraborty/) 6 Answer (http://theconstructor.org/questions/grade-concrete-m20-m25-roof-casting-cement-required1m3-concrete/#comments) 5603 views Answers ( 6 ) Gopal Mishra (http://theconstructor.org/author/gopal­mishra/) http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 2/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? Gopal Mishra (http://theconstructor.org/author/gopal­mishra/) Jun 2, 2016 at 12:16 (http://theconstructor.org/questions/grade­concrete­m20­m25­ roof­casting­cement­required­1m3­concrete/#comment­26019) Hi Pal Chakraborty, As seen from image you have attached, I have estimated that the roof area of 66.2 Square Meter and deduction of 3.62 square meter for staircase area as shown in plan you have provided. So, net area of RCC Slab is taken as 62.58 square meter. Though image is not clear, I have taken the dimensions as it appeared to me. You have also not mentioned the thickness of reinforced concrete slab. I have assumed that the slab has a thickness of 150mm. Thus the total volume of concrete required by you 62.58*0.15 = 9.387 cubic meter of concrete. If you use the nominal concrete mix, the generally used concrete in residential building is M20 with cement : sand : aggregate proportion as 1 : 1.5 : 3. Thus, for the given mix proportion, the quantity of cement required is 7.9 bags per cubic meter of concrete. So, the total quantity of cement required for your M20 roof construction of 150mm thickness should be 74.157 bags of cement. If your mason has used only 60 bags of cement, then he has not used http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 3/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? If your mason has used only 60 bags of cement, then he has not used M20 concrete for your roof construction. If we consider M15 concrete, the mix proportion is 1 : 2 : 4. One cubic meter of M15 concrete requires 6.2 bags of cement. Thus for 9.387 cubic meter, cement bags required will be 58.2 bags. Thus, your mason has used the ratio of cement sand and aggregates close to M15 concrete. As per Indian Standard, the minimum grade of concrete for residential reinforced work shall be M20. Refer this table for quantities of material required per meter cube of concrete (http://theconstructor.org/practical­guide/estimated­quantities­ of­materials­required­per­cubic­metre­of­compacted­mortar­or­ concrete/1304/). Best answer Pal Chakraborty (http://theconstructor.org/profile/pal­chakraborty/) Jun 3, 2016 at 08:58 (http://theconstructor.org/questions/grade­concrete­m20­m25­ roof­casting­cement­required­1m3­concrete/#comment­26026) Dear Gopal, http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 4/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? As per as the following document(p­20, Table: 5) cement required for M20 grade concrete is 320 kg/cum. http://www.nitsri.net/Civil/course­material/IS%20456­2000.pdf (http://www.nitsri.net/Civil/course­material/IS%20456­2000.pdf) Please let me know your view Gopal Mishra (http://theconstructor.org/author/gopal­mishra/) Jun 3, 2016 at 13:42 (http://theconstructor.org/questions/grade­concrete­m20­m25­ roof­casting­cement­required­1m3­concrete/#comment­26028) Dear Pal, The table 5 of IS456:2000 specifies the minimum quantity of cement required for different grades of concrete. This does not mean that minimum quantity of cement has to be used for the construction. During the mix design calculation, if the cement required is below 300 kg/m3 of concrete, then 300 kg/m3 is only taken as the cement content. Let us take an example to find out the cement quantity calculation for M20 Concrete. Cement Calculation for M20 (1:1.5:3 ) http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 5/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? Cement Calculation for M20 (1:1.5:3 ) Concrete: For a normal reinforced concrete slabs, the medium workability of concrete required. This corresponds to 50 to 10mm slump value (Refer Page­7, IS456:2000). Consider, the slump value required in our case as 75mm for a good workable concrete with use of vibrator. If vibrator is not used, then 100mm slump should be considered. Refer Table­2, section 4.2 page 2 of IS 10262­2009. This section provides the details for maximum quantity of water to be used for 20mm aggregates for slump 25 to 50mm. In our case slump considered is 75mm. So, quantity of water required is: Water content = 186 + (3/186)x100 = 191.6 kg (liters) (increase water content by 3%) Thus, if we consider a water cement ratio of 0.5, then quantity of cement required = 191.6/0.5 = 383.2 kg (7.66 bags of cement). Thus, 383.2 kg of cement is greater than 300 kg minimum as per IS456. http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 6/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? Remember, we have considered only a slum of 75mm, generally used slump in residential construction is 100mm. Also, we have assumed a water­cement ratio of 0.5, for better strength normally 0.45 is used. So, if you consider 100mm slump and 0.45 water cement ratio, then water quantity required = 186 + (6/186)x100 = 197.16 kg of water Cement quantity required = (197.16 / 0.45 ) = 425.8 kg (8.5 bags)/m3 of concrete. The maximum quantity of water is considered in this example. There are many factors which influence the calculation of water and cement quantities for 1 cubic meter of concrete. This calculation is just to get an idea. Above example is the most simplest method of cement quantity calculation. Hope, I answered your question. You can also refer calculations section ANNEX­A of IS 10262­2009 (https://law.resource.org/pub/in/bis/S03/is.10262.2009.pdf). Pal Chakraborty (http://theconstructor.org/profile/pal­chakraborty/) Jun 3, 2016 at 15:24 (http://theconstructor.org/questions/grade­concrete­m20­m25­ roof­casting­cement­required­1m3­concrete/#comment­26029) http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 7/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? Dear Gopal, Thanks a lot for your clarifications. Could you please let me know what are the problems I shall face due to the construction of roof with M15 standard concrete? Please let me know do I need to break the casting and re­construct? Please suggest me some remedy to prevent any damage in future. Gopal Mishra (http://theconstructor.org/author/gopal­mishra/) Jun 4, 2016 at 00:17 (http://theconstructor.org/questions/grade­concrete­m20­m25­ roof­casting­cement­required­1m3­concrete/#comment­26030) Hi Pal, There can be problems and there may not be any problem with M15 grade concrete in RCC roof. It all depends on the structural design of slab. For structural design of slab following factors are considered: (/) 463 Live load on Slab SHARES Self weight of slab Facebook (http://www.facebook.com/sharer.php?u=http://theconstructor.org/questions/grade-concrete-m20-m25-roof-castingcement-required-1m3-concrete/) Finishing weight on slab Twitter (https://twitter.com/intent/tweet? text=What+Grade+of+Concrete+%28M20%2FM25%29+used+in+RCC+Roof+Casting%3F&via=theconstructor2&url=http://theconstructor.org/question Span of Slab concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 8/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? text=What+Grade+of+Concrete+%28M20%2FM25%29+used+in+RCC+Roof+Casting%3F&via=theconstructor2&url=http://theconstructor.org/question Span of Slab concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) Google (https://plus.google.com/share?text=What Grade of Concrete (M20/M25) used in RCC Roof Casting? Its length / width ratio (to determine one­way or two­way slab) &url=http://theconstructor.org/questions/grade-concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) Based on all the above data, when we calculate the reinforcement required for a M15 concrete, and compare it with the reinforcement provided, then only we can say whether the slab is fit for its intended purpose or not. Whether the slab is safe for the live load considered or not. So, Just by knowing that concrete of M15 has been used, it does not make the roof slab unsafe. We have to technically prove that the slab is unfit for the intended purpose only by calculation. Prior to IS456­2000, the then M20 concrete mix proportion was current M15 mix proportion (i.e. 1:2:4). But considering the poor workmanship and quality control at construction site, the M20 concrete mix proportion was changed to 1:1.5:3 just to make sure the RCC structure has enough strength even in the worst conditions of poor quality control. So, hope that if the quality of construction is good for your roof slab, then (/) 463 SHARES this should not cause any problem. But, I am not able to clearly say whether it is suitable or unfit as I do not have required data. Facebook (http://www.facebook.com/sharer.php?u=http://theconstructor.org/questions/grade-concrete-m20-m25-roof-castingcement-required-1m3-concrete/) Twitter (https://twitter.com/intent/tweet? text=What+Grade+of+Concrete+%28M20%2FM25%29+used+in+RCC+Roof+Casting%3F&via=theconstructor2&url=http://theconstructor.org/question concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 9/20 9/10/2016 What Grade of Concrete (M20/M25) used in RCC Roof Casting? text=What+Grade+of+Concrete+%28M20%2FM25%29+used+in+RCC+Roof+Casting%3F&via=theconstructor2&url=http://theconstructor.org/question concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) Google (https://plus.google.com/share?text=What Grade of Concrete (M20/M25) used in RCC Roof Casting? Tenzin Dorji (http://theconstructor.org/profile/tenzin­dorji/) &url=http://theconstructor.org/questions/grade-concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) Aug 20, 2016 at 16:27 (http://theconstructor.org/questions/grade­concrete­m20­m25­ roof­casting­cement­required­1m3­concrete/#comment­26150) Hi Gopal, thank you for the information. but the data shown in table shows that weight in kg is 395kg of cement for M20 and interms of bag its 7.9 bags. that means the total kgs for per cubic meter is equal to 3120kgs? Leave An Answer Name * E-Mail * Attachment Choose File No 䕕ሥle chosen Select file (/) Browse 463 Comment * SHARES Facebook (http://www.facebook.com/sharer.php?u=http://theconstructor.org/questions/grade-concrete-m20-m25-roof-castingVisual cement-required-1m3-concrete/) Twitter (https://twitter.com/intent/tweet? Text text=What+Grade+of+Concrete+%28M20%2FM25%29+used+in+RCC+Roof+Casting%3F&via=theconstructor2&url=http://theconstructor.org/question concrete-m20-m25-roof-casting-cement-required-1m3-concrete/) http://theconstructor.org/questions/grade­concrete­m20­m25­roof­casting­cement­required­1m3­concrete/ 10/20