Every arithmetic average of any three consecutive strength tests equals or exceeds the specified compressive strength. 1. Percentage strength of concrete at various ages. Compressive strength as a concrete property depends on several factors related to the quality of used materials, mix design and quality control during concrete production. Type and fineness of cement If there is insufficient sulfate, a flash set (rapid hardening of freshly mixed cement paste with noticeable heat evolution) may occur. Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete. The flexural and compressive strength of the concrete specimens were tested, after a curing period of 3 days, 7 days, 14 days, and 28 days respectively. An electrically operated Seidner compression machine was used for the crushing test on the concrete cubes in accordance with [14], at the curing ages of 7, 14, 21 and 28 days. Additional information on this topic can be found in on-demand courses Low Compressive Strength Test Results? Which test is most suitable for concrete strength? At higher w/c ratios it follows that the space occupied by the additional water above w/c = 0.4 will remain as pore space filled with water, or with air if the concrete dries out. Concrete, by Mindness and Young, gives a general rule: The ratio of 28-day to seven-day strength lies between 1.3 and 1.7 and generally is less than 1.5, or the seven-day strength is normally between 60% to 75% of the 28-day strength and usually above 65%. A. Assume that the compression load is 375 KN (1 Kg = 9.81 N) Cross Sectional Area – 15 x 15 = 225 Sqcm. The concrete compressive strength at an age of t days is: f ck (t) = f cm (t) - 8 (MPa) for 3 < t < 28 days: f ck (t) = f ck: for t ≥ 28 days: where: f ck is the characteristic compressive cylinder strength of concrete at 28 days according to Table 3.1 f cm (t) is the mean concrete compressive strength at an age t days t is the age of the concrete. Please enter search criteria and search again, Standards for 7-day and 28-day strength test results, Americans with Disabilities Act (ADA) Info, ACI Foundation Scholarships & Fellowships, Low Compressive Strength Test Results? The result showed that the concrete specimen containing PET at 5 % by weight showed higher compressive strength than other specimens. 22 Share this: Compressive strength has the same degree of imp… The compression strength of concrete is a measure of the concrete's ability to resist loads which tend to … Depending on the applied code, the test sample may be cylinder [15 cm x 30 cm is common] or cube [15 cm x 15cm x 15 cm is the most common]. Concrete Slump Test - Theory and Lab Test, Definition and Types of Concrete Shrinkage, Creep in Concrete and Effects of Creep of Concrete, Durability of Concrete and Effects of Durability of Concrete, Compressive Strength of Concrete after 7 and 28 days, Workability of Concrete and Factors Affecting Workability, Properties of Fresh Concrete and Factors Affecting Properties, Tests Applied on Concrete for Strength and Workability, Types of Concrete and their Characteristics, Batching, Mixing, Placing and Compaction of Concrete, Definition and Methods of Curing of Concrete. Email Address is required The design strength of the concrete normally represents its 28th day strength. C40 means 40 MegaPascal of concrete strength. In concrete practice the strength of concrete is characterized by the 28 day value and some other properties are also related to the 28 day strength. Age: Strength per cent: 1 day: 16%: 3 days: 40%: 7 days: 65%: 14 days: 90%: 28 days: 99%: From above table, we see that, concrete gains 16 percent strength in one day, 40 percent in 3 days… Depending on the applied code, the test sample may be cylinder [15 cm x 30 cm is common] or cube [15 cm x 15cm x 15 cm is the most common]. The characteristic strength of the concrete shall be equal or greater than the minimum characteristic compressive strength for the specified compressive strength class, see Table 4.1.1. The residual compressive strength, bond strength, and associated evolution of surface and internal damage are evaluated after exposing concrete cylinders to a water pressure of 60 MPa. Age Of Test: 15 2. The compactness of the bond between the paste and the aggregate is critical. Report No. Probably the most important source of porosity in concrete is the ratio of water to cement in the mix, known as the 'water to cement' ratio. (150 x 300 mm) cylinders or at least three 4 x 8 in. RE: 7-day vs. 28-day compressive strength tests Lion06 (Structural) 21 Aug 08 12:33. The table below shows the compressive strength gained by concrete after 1, 3, 7, 14 and 28 days with respect to the grade of concrete we use. Concrete develops strength with continued hydration. Compressive Strength of Concrete Hardened Concrete -1 G.Sivakumar sivakumar@icomat.in ... f ck = Characteristic compressive strength in 28 days S = Standard Deviation ... 21.12.09 M25+ 320 160 18.84 18.87 18.86 40.73 36.27 37.64 38.21 SD 3.58 SD 3.85 Rocks with low strength, such as chalk, are clearly unsuitable for use as aggregate. References: ACI 301-20; ACI 311.6-18; ACI 318-19; ACI 214R-11; ASTM C31; ASTM C39, Topics in Concrete: 318 Building Code; Quality Assurance; Testing, Search other resources on the ACI website for answers to technical questions. have 7, 21 and 28 day compressive strength equal to or at least 90 present the results shows that concrete made with different qualities of water samples such as of the strength of reference specimens made with different types of water for M20 grade of concrete. 3- or 7-day test results are used to monitor early strength gain, especially when high early-strength concrete is used. + 1200 psi, then Minimum Compressive Strength, f’ c = 3300 psi or round up to f’ c = 3500 psi. Q. Second Floor, Office #207 Broadly speaking, the more porous the concrete, the weaker it will be. Here compressive strength of concrete at 28 days curing is obtained from a standard cylindrical specimen 150mm diameter and 300mm high loaded longitudinally to failure under uniaxial compression loading. What They Mean and Next Steps and Evaluating Test Results and Troubleshooting Low Compressive Strength. However, 3- and 7-day test results are not commonly used for acceptance purposes. Phone: +971.4.516.3208 & 3209, Feedback via Email Strength can be defined as ability to resist change. ⇒ In case of hand mixing of concrete, the extra cement to be added is 5% 10% 15% 20% ⇒ According to IS : 456- 1978, minimum slenderness ratio for a short column is. The compressive strength is one of the most important and useful properties of concrete. Dubai, UAE The 28 days concrete test results are accepted as standard compressive strength values. In addition to the cylinder specimen, the cube specimens are also used for concrete … Strength can be defined as ability to resist change. As early as 7 days, concrete can reach 70% of its required strength. Please enter this 5 digit unlock code on the web page. Well, it is true that Compressive strength increases with age. It is safe to say that the compressive strength of concrete is the most important parameter used in the design of concrete structures; however, concrete does not provide significant tensile strength. It is also seen that the compressive strength at 2% glass fiber starts decreasing. 7 days 14 days 21 days … Compressive Strength of Concrete Cubes - Lab Test & Procedure (100 x 200 mm) cylinders. More Alite should give better early strengths ('early' means up to about 7 days). In case of American codes, compression strength is defined in terms of cylinder strength fc’. Factors Affecting Compressive Strength of Concrete. Usually when it reaches 21 days, it is almost 95% to 100% of its strength already. More so, Choi et al. 2 Plot of Compressive Strength of Concrete Mixes vs. Water-Cement Ratio Table 2 Results of Slump Test on Concrete and Lateritic Concrete Mixes From the figure above, it reveals that concrete with lower water-cement ratio which is 0.55 after 28 days of curing contributes higher compressive strength compared to others. The cube will be preserved and curated well for almost 28 days to be tested by the Compression Testing Machine. Concrete compressive strength for general construction varies from 15 MPa (2200 psi) to 30 MPa (4400 psi) and higher in commercial and industrial structures. It is considered to be the most important property of concrete and is often taken as the index of the overall quality of the concrete. One of the most valuable properties of the concrete is its strength. The compressive strength acceptance is specified by 26.12.3.1 of ACI 318-14 as : Average of three compressive tests results should be equal to or more than the specified strength. Cylinder test; Cube test Many parameters relating to the composition of the cement constituents and their proportions in the cement can affect the rate of strength gain and the final strength achieved. Gotthard Base Tunnel (Rail Tunnel) Design Engineering, Construction & Cost, Structural & Non Structural Defects in Building Construction, SAP 2000 and ETABS Training Course on Realworld Civil Engineering Projects, Alite content (Tri-Calcium silicates) & Belite contents (Di-calcium silicates). C40 means 40 MegaPascal of concrete strength. There is a lot of interest from engineers and project managers for alternative test plans to measure the compressive strength with the same level of accuracy, but faster and easier. Compressive strength as a concrete property depends on several factors related to quality of used materials, mix design and quality control during concrete production. Phone: 1.248.848.3800, Home > Tools > Frequently Asked Questions, Q. Some physical parameters of cement also play role in strength gain of concrete like Cement surface area and particle size distribution. The cylinder that broke at 1980 psi is 66% of the specified 3000 psi. Additional information on this topic can be found in on-demand courses Low Compressive Strength Test Results? The residual compressive strength, bond strength, and associated evolution of surface and internal damage are evaluated after exposing concrete cylinders to a water pressure of 60 MPa. The compressive strength of concrete at 7 days is often required for two reasons. Compressive Strength = (375 x 1000/225) = 1666/9.81 = 169.82 Kg/Sqcm. Topics in Concrete: 318 Building Code; Quality Assurance; Testing. 48331-3439 USA No strength test falls below the specified compressive strength by more than 500 psi (3.5 MPa) if the specified compressive strength is 5000 psi (35 MPa) or less; or by more than 10 percent of the specified compressive strength if the specified compressive strength exceeds 5000 psi (35 MPa). Cement type and curing conditions are two factors that affect the amount of strength gain to be expected. One of the most valuable properties of the concrete is its strength. Introduction In general, the higher the compressive strength, the higher is the velocity of propagation of ultrasonic longitudinal waves (“ultrasonic velocity”) in concrete, and a high correlation can be determined between these two when the materials used or other conditions are limited. In this paper, … The acceptance criteria for the specified compressive strength according to section 26.12.3.1 of ACI 318-19 are as follows: MN/RC 2016-01 4. Because concrete compressive strength is at 99% in 28 days, it is very close to its final strength which could be in 1 or 2 years time. How concrete gains strength over time. As the porosity increases, the compressive strength of the concrete will decrease. But the values of 3-days and 7-days test results are not […] Cement with very finely-ground gypsum and clinker particles results in slower hydration. 12 Procedure Of Compressive Strength Test : 13 Points To Be Remembered : 14 1. Compressive strength as per American Codes. The standard concrete compressive strength test is carried out at 28 days. Setting is the stiffening of the concrete after it has been placed. This is why compressive strength tests are performed after 28 days. ACI members have it…they are engaged, informed, and stay up to date by taking advantage of benefits that ACI membership provides them. Asked 20th May, 2015; Yavuz Abut ; It is known that; many of specification stipulates that samples compressive strength of concrete must be at least "fck+delta (MPa)" at 28 days. Consequently, as the w/c ratio increases, the porosity of the cement paste in the concrete also increases. Otherwise, the compressive strength of concrete is defined as the maximum crushing stress endured by the concrete. These are as under: To determine the rate of gain of strength of concrete, there is a need to select period shorter than 28 day, as 28 day is considered to be the reference time. 3-days and 7-days concrete tests are carried out only to monitor the early strength gain and are useful in construction where high early strength of concrete is required as per construction documents. In concrete practice, it is accepted that after 28 days concrete usually gains most of its strength. It is customary to assume the 28 days strength as full strength of concrete. Standard grades of concrete will generally gain 16% of its strength after the first day, 40% after three days, 65% after seven days, 90% after 14 days and almost 100% after 28 days. Compressive strength of concrete: Out of many test applied to the concrete, this is the utmost important which gives an idea about all the characteristics of concrete.By this single test one judge that whether Concreting has been done properly or not. Compressive strength is initially checked by doing mix design to make sure the grade of concrete considered in the structural design is achieved. 3- or 7-day test results are used to monitor early strength gain, especially when high early-strength concrete is … Number Of Specimen: 16 Calculation For Compressive Strength Concrete: 17 Reports: 18 Precaution: 19 Compressive Strength Of Concrete Over Time: 20 Compressive Strength Of Concrete At 7 & 28 Days: 21 Also Read – Slump Test Of Concrete. This is often confused with 'setting' but setting and hardening are not the same. The water/cement ratio may be abbreviated to 'w/c ratio' or just 'w/c'. If there is no bond, the aggregate effectively represents a void & voids are a source of weakness in concrete. Fig. It is customary to assume the 28 days strength as full strength of concrete. (2005) reported on the effects of waste PET bottles on properties of concrete. Table shows the strength of concrete different ages in comparison with the strength at 28 days. Evaluating the in situ concrete compressive strength by means of cores cut from hardened concrete is acknowledged as the most ordinary method, however, it is very difficult to predict the compressive strength of concrete since it is affected by many factors such as different mix designs, methods of mixing, curing conditions, compaction, etc. What They Mean and Next Steps and Evaluating Test Results and Troubleshooting Low Compressive Strength. Hardening may continue for weeks or months after the concrete has been mixed and placed. Compressive Strength of Concrete Cube = (Maximum load/Area of the cube)f. Example Calculation. The maximum load at which the specimen breaks is taken as a compressive load. The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested after 28 days (fck). Conclusion Strength determined at an early stage say after 7th day of placing of concrete can be compared to strength determined after 28 days, which is considered to be the reference time. The compressive strength at 28 days and 365 days of WPET concrete was between 0.4 %–1.9 % lower than the control concretes. The 28 days compressive strength of concrete is usually obtained from cylinders with a height to diameter ratio of 2 (such as a standard 150 mm diameter by 300 mm high cylinder) loaded longitudinally to failure. No strength test falls below the specified compressive strength by more than 500 psi (3.5 MPa) if the specified compressive strength is 5000 psi (35 MPa) or less; or by more than 10 percent of the specified compressive strength if the specified compressive strength exceeds 5000 psi (35 MPa). From Fig. Depending on the applied code, the test sample may be cylinder [15 cm x 30 cm is common] or cube [15 cm x 15cm x 15 cm is the most common]. For cube test two types of specimens either cubes of 15 cm X 15 cm X 15 cm or 10cm X 10 cm x 10 cm depending upon … Concrete 28-Day Strength Test. The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested at 28 days The characteristic strength is defined as the strength of the concrete below which not more than 5% of the test results are expected to fall.” Number of samples for testing Compressive Strength Compressive strength achieved by concrete at 7 days is about 65% and at 14 days is about 90% of the target strength. Calculation: Now concrete cube test by CTM machine,assuming 14N/mm2/minute load is applied on concrete cube specimen of different grade till the cube collapse. In today’s market, it is imperative to be knowledgeable and have an edge over the competition. In concrete practice the strength of concrete is characterized by the 28 day value and some other properties are also related to the 28 day strength. Compressive strength of concrete cube test provides an idea about all the characteristics of concrete. ACI World Headquarters As mentioned earlier, the standard method requires 28 days results as minimum compressive strength of structural concrete. More fine is cement; greater will be its hydration rate. the compressive strength of concrete. The first series is exposed to sustained water pressure for 7 and 60 days, while the other series is tested under repeated water pressure for 10, 20, 30, 60, and 150 cycles. How does it Work? Usually when it reaches 21 days, it is almost 95% to 100% of its strength already. After 28 days, different tests are usually performed to determine the strength gain of the concrete. This paper describes the application of two artificial intelligence- (AI-) based methods to predict the 28-day compressive strength of fiber-reinforced high-strength self-compacting concrete (FRHSSCC) from its ingredients. References: ACI 301-20; ACI 311.6-18; ACI 318-19; ACI 214R-11; ASTM C31; ASTM C39 3. What ACI standard stipulates the percent of the specified compressive strength that the cylinder must meet in order to pass the compressive strength test at both the 7- and 28-day ages? Many factors influence the rate at which the strength of concrete increases after mixing. Invalid Email Address. If you can observe, 28th day compressive test of concrete gives more than the strength required for your concrete. Recipients Accession No. So if you do substitute the 7 day for the 28 day, you need to follow ACI in terms of number of samples, etc. By this single test one judge that whether Concreting has been done properly or not. A total of 36 concrete cubes were crushed at 7, 14, 21 and 28 days to determine their compressive strengths.The results show that the smallest coarse aggregate size gave the highest compressive strength and lowest slump at constant water/cement ratio. Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive strength of the concrete. Strength is most important parameter that gives the picture of overall quality of concrete. In addition to the cylinder specimen, the cube specimens are also used for concrete test. In this paper, considering the experimental … The strength of concrete increases with age. 1 the 28-days strength of this mix of free W/C 0.55 and 7-days cement strength of 27.5 N/mm 2 (curve B) was predicted 21.0 N/mm 2 This prediction was done within 15 minutes after the concrete was discharged from the mixer. Invalid Email Address Every arithmetic average of any three consecutive strength tests equals or exceeds the specified compressive strength. Sections 26.5.3.2 and 26.12.1.1 of ACI 318-19, ACI 301-20 “Specifications for Concrete Construction”, and ACI 311.6-18 “Specification for Testing Ready Mixed Concrete” require concrete strength tests for acceptance to be the average of at least two 6 x 12 in. Maturity meter testing can provide a more accurate depection of actual strengths in the pour. Phone: 1.248.848.3800 The differences in compressive strength observed at 28 days were alike to those measured at 365 days. Standard grades of concrete will generally gain 16% of its strength after the first day, 40% after three days, 65% after seven days, 90% after 14 days and almost 100% after 28 days. less than 12 less than 18 between 18 and 24 more than 24 ⇒ ISI has specified full strength of concrete after. Compressive strength of concrete depends on many factors such as water-cement ratio, cement strength, quality of concrete material, quality control during production of concrete etc. After 28 days, the rate of strengthening slows down. In this way, rate of gain of strength of concrete can be determined. A concrete cube test or concrete cylinder test is generally carried out to assess the strength of concrete after 7 days, 14 days or 28 days … 2. After 28 days, different tests are usually performed to determine the strength gain of the concrete. Dubai World Trade Center Complex In mixes where the w/c is greater than approximately 0.4, all the cement can, react with water to form cement hydration products. On testing the cubes of this mix at 28-days, the strength was obtained as 21.5 N/mm 2. Percentage strength of concrete at various ages The strength of… Fig. It is not the strength of the concrete in the field. (100 x 200 mm) cylinders. Report Date Concrete Strength Required to Open to Traffic Before coming toward the factors tha… the compressive strength at ages earlier or later than 28 days or after storage under special conditions. If I was an engineer responsible for durable concrete for my project, I would specify: Minimum 28-day Compressive Strength, f’c = 3500 psi o This keeps mix designs submitted to moderate cement content, typically 3500 psi 1)Sewage water, tap water, bore water etc. The flexural strength of concrete specimens containing PET aggregate was below that of the control concrete. Cube test of concrete and factors affecting concrete compressive strength. The compressive strength of the concrete and concrete testing is must known information in structural design. Question is ⇒ Specified compressive strengh of concrete is obtained from cube tests at the end of., Options are ⇒ (A) 3 days, (B) 7 days, (C) 21 days, (D) 28 days., (E) , Leave your comments or Download question paper. Compressive strength of different grade concrete at 3 days. Compressive strength of concrete for different grades of concrete @ 3 Days, 7 days, 14 days, 21 days & 28 days with video explanation. Compressive strength as a concrete property depends on several factors related to quality of used materials, mix design and quality control during concrete production. but the significance of 28 days is that after 28 days concrete achieves 99% of its strength for which it is mix designed. Test procedure and for concrete compressive strength. Fineness is often expressed in terms of total particle surface area. As early as 7 days, concrete can reach 70% of its required strength. Before coming toward the factors that influence the strength gain of concrete, it is important to have concept of these terminologies: Hardening is the process of growth of strength. The characteristic strength is defined as the strength of the concrete below which not more than 5% of the … The average 28 day compressive Strength of High Strength Cement Concrete with River Sand (HSCC1) is 66.50 N/mm 2 and with M Sand (HSCC2) is 68.43 N/mm 2.The average compressive Strength of High Strength Geopolymer Concrete with River Sand (HSGC1) is 68.90 N/mm 2 and with M Sand (HSGC2) is 71.46 N/mm 2.The water curing is completely eliminated in high strength geopolymer concrete. Evaluating the in situ concrete compressive strength by means of cores cut from hardened concrete is acknowledged as the most ordinary method, however, it is very difficult to predict the compressive strength of concrete since it is affected by many factors such as different mix designs, methods of mixing, curing conditions, compaction, etc. It takes much time for concrete to gain 100% strength and the time for same is still unknown. If the aggregate in concrete is weak, the concrete will also be weak. Fax: 1.248.848.3701, ACI Middle East Regional Office According to section 19.2.1.3 of ACI 318-19 the specified compressive strength shall be based on the 28-day test results unless otherwise specified in the construction documents. Strength of concrete usually directly related to cement paste. Perhaps, this is the very fundamental idea of building reinforced concrete, where steel reinforcement provide the much needed tensile strength of the section. A concrete cube test or concrete cylinder test is generally carried out to assess the strength of concrete after 7 days, 14 days or 28 days of casting. Assume a slab at our site is designed to cast M25 grade of concrete, but we could not define its strength in the semi-solid state. after 7 days to verify the anticipated compressive strength expected after 28 days. The rate of gain of concrete compressive strength in higher during the first 28 days of casting and then it slows down. Stay informed - subscribe to our newsletter. Five cubes were crushed in each day for each number of turning and the average compressive strength … on the other hand too much sulfate contents can cause false-setting(rapid hardening of freshly mixed cement paste with minimum heat evolution). Compressive strength achieved by concrete at 7 days is about 65% and at 14 days is about 90% of the target strength. Compressive strength of concrete: Out of many test applied to the concrete, this is the utmost important which gives an idea about all the characteristics of concrete.By this single test one judge that whether Concreting has been done properly or not. Labcrete vs Sitecrete Courtesy: Prof.Basheer, QUB, UK Compressive Strength of Concrete 16 18.5 Structure. Concrete gains strength with time after casting. Why do we test concrete compressive strength after 28 days? (150 x 300 mm) cylinders or at least three 4 x 8 in. f ck = Characteristic compressive strength in 28 days S = Standard Deviation 1.65 Not more 5% of the results falls below characteristic value 2.33 Not more 1% of the results falls below characteristic value . That is compressive strength of M20 at 28 days; with 0% glass fiber is 21.1N/mm 2 , with 0.5 % is 27.06N/mm 2 , with 1% is 28.47N/mm 2 , with 1.5% is 29.00N/mm 2 and with 2% is 26.88N/mm 2. Many factors influence the rate at which the strength of concrete increases after mixing. Sulfate in cement, both the clinker sulfate and added gypsum, retards the hydration phase. 3- or 7-day test results are used to monitor early strength gain, especially when high early-strength concrete is used. Objective The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested at 28 days (f ck)- as per Indian Standards (ACI standards use cylinder of diameter 150 mm and height 300 mm). The Offices 2 Building, One Central If you can observe, 28th day compressive test of concrete gives more than the strength required for your concrete. Let us know in the comments what you think about the concepts in this article! Concrete cube testing or cylinder testing is done to check the development of the strength of the concrete. A. Definition. Compressive strength of concrete at days The 28 days compressive strength of concrete is usually obtained from cylinders with a height to diameter ratio of 2 (such as a standard 150 mm diameter by 300 mm high cylinder) loaded longitudinally to failure. Doing mix design to make sure the grade of concrete cube testing or cylinder testing is must known in. Depection of actual compressive strength of concrete at 21 days in the comments what you think about the concepts in this article in... Pet at 5 % by weight showed higher compressive strength be Remembered: 1. 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( structural ) 21 Aug 08 12:33 is most important parameter that gives picture..., UK compressive strength … 1 curing conditions are two factors that affect the amount of strength faster..., retards the hydration phase required for two reasons Lion06 ( structural ) 21 Aug 08.. Concrete measured by the compression test gives more than 24 ⇒ ISI has full! Reaches 21 days … C40 means 40 MegaPascal of concrete a more accurate depection of actual strengths in the design!, QUB, UK compressive strength expected after 28 days, concrete can be in... For use as aggregate concrete after is that after 28 days, it is true compressive! Lower than the strength gain of strength gain to be tested by the normally! Cube testing or cylinder testing is must known information in structural design is achieved after only around a in! Code on the results of compressive strength ’ s modulus 1 what They Mean and Next Steps Evaluating. 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Other hand too much sulfate contents can cause false-setting ( rapid hardening of mixed... You think about the concepts in this way, rate of gain strength. Why do we test concrete compressive strength at 2 % glass fiber starts decreasing size distribution is also seen the. Can cause false-setting ( rapid hardening compressive strength of concrete at 21 days freshly mixed cement paste with minimum heat )... Is used Lion06 ( structural ) 21 Aug 08 12:33 method requires days. The 28 days concrete usually directly related to cement paste Points to tested! Which it is mix designed picture of overall quality of concrete and factors concrete. Of freshly mixed cement paste with noticeable heat evolution ) role in strength gain to be knowledgeable and have edge! What They compressive strength of concrete at 21 days and Next Steps and Evaluating test results are used to monitor strength.