CN114235565B - Method for estimating 28d strength of concrete - Google Patents
Method for estimating 28d strength of concrete Download PDFInfo
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- CN114235565B CN114235565B CN202111293483.5A CN202111293483A CN114235565B CN 114235565 B CN114235565 B CN 114235565B CN 202111293483 A CN202111293483 A CN 202111293483A CN 114235565 B CN114235565 B CN 114235565B
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- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000004570 mortar (masonry) Substances 0.000 claims abstract description 99
- 238000012360 testing method Methods 0.000 claims abstract description 54
- 239000000463 material Substances 0.000 claims abstract description 15
- 238000002156 mixing Methods 0.000 claims abstract description 15
- 239000002994 raw material Substances 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 37
- 239000004568 cement Substances 0.000 claims description 33
- 239000004576 sand Substances 0.000 claims description 15
- 238000010998 test method Methods 0.000 claims description 8
- 238000005259 measurement Methods 0.000 claims description 7
- 238000003756 stirring Methods 0.000 claims description 6
- 239000003795 chemical substances by application Substances 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 238000011049 filling Methods 0.000 claims description 3
- 238000012423 maintenance Methods 0.000 claims description 3
- 239000010705 motor oil Substances 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 claims description 2
- 238000007599 discharging Methods 0.000 claims 1
- 238000000465 moulding Methods 0.000 claims 1
- 238000004519 manufacturing process Methods 0.000 abstract description 5
- 239000002699 waste material Substances 0.000 abstract description 5
- 238000002360 preparation method Methods 0.000 description 8
- 239000003638 chemical reducing agent Substances 0.000 description 5
- 239000010881 fly ash Substances 0.000 description 5
- 239000000843 powder Substances 0.000 description 5
- 238000010276 construction Methods 0.000 description 4
- 229910052500 inorganic mineral Inorganic materials 0.000 description 4
- 239000011707 mineral Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000009835 boiling Methods 0.000 description 3
- 239000000701 coagulant Substances 0.000 description 2
- 230000002035 prolonged effect Effects 0.000 description 2
- 238000003908 quality control method Methods 0.000 description 2
- 239000002893 slag Substances 0.000 description 2
- 239000004575 stone Substances 0.000 description 2
- 239000011800 void material Substances 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- 239000011398 Portland cement Substances 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000003823 mortar mixing Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000010025 steaming Methods 0.000 description 1
- 239000008399 tap water Substances 0.000 description 1
- 235000020679 tap water Nutrition 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/36—Embedding or analogous mounting of samples
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
- G01N2203/0003—Steady
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
Abstract
The invention discloses a method for estimating 28d strength of concrete, which belongs to the technical field of concrete and mainly comprises the following steps: (1) preparing mortar; (2) mortar curing; (3) measuring the compressive strength of the mortar 7 d; (4) Calculating a mortar surplus coefficient according to the mixing ratio and the density of the raw materials; (5) estimating the compressive strength of the concrete 28 d: f (f) 28 ＝aγ+bf m,7 ‑50.5γ 2 ‑0.03f m,7 2 -271.8; wherein f 28 -concrete 28d compressive strength (MPa); f (f) m，7 -mortar 7d compressive strength (MPa); the gamma-mortar surplus coefficient is directly adopted to estimate the strength of the concrete 28d by adopting the 7d mortar strength, so that the operation process can be simplified, meanwhile, the material waste caused by manufacturing a concrete cube test piece is avoided, the correlation coefficient of the estimated function is large, the stability is good, the required time is short, the fitting degree is good, and the rapid reference can be provided for the concrete quality pre-judgment and the mixing ratio adjustment in engineering.
Description
Technical Field
The invention relates to the technical field of concrete, in particular to a method for estimating the 28d strength of concrete.
Background
The quality of concrete is the key of engineering quality control, and the compressive strength of concrete is the core of concrete quality control, so guaranteeing concrete strength is particularly important in engineering construction. The existing standard is to take the compressive strength of the cube of the standard curing 28d as the concrete strength, so that the required period is longer, the engineering progress is influenced, the concrete cube test piece is larger, more raw materials are required, the resource waste is caused, and the workload is also larger. With the development of the construction industry, the demand for concrete is increasing, the construction process of concrete is also increasing, and a simple and rapid method is urgently needed to estimate the compressive strength of the concrete 28 d. Therefore, a simple test method for early estimating the strength of concrete is required. According to the data, the following test methods for early estimating the strength of concrete are mainly available at present:
1. boiling water method: and (3) after the concrete test piece is molded and stood, immersing the concrete test piece in boiling water for curing, and measuring the strength of the accelerated curing concrete test piece, thereby estimating the standard curing 28d concrete strength.
2. Hot water process 80 deg.c: and (3) after the concrete test piece is molded and stood, immersing the concrete test piece in hot water at 80 ℃ for curing, and measuring the strength of the accelerated curing concrete test piece so as to estimate the standard curing 28d concrete strength.
3. Wen Shuifa 55 ℃ C.): and (3) after the concrete test piece is molded and stood, immersing the concrete test piece in warm water at 55 ℃ for curing, and measuring the strength of the accelerated curing concrete test piece, thereby estimating the standard curing 28d concrete strength.
4. Mortar accelerating and steaming method: screening mortar in the concrete mixture, adding a coagulant, forming a test piece, then placing the test piece in high temperature and high pressure for curing, and measuring the strength of the test piece for accelerating curing of the mortar, thereby estimating the compressive strength of the standard curing 28d concrete.
5. Early-age method: a method for estimating the standard curing 28d concrete strength by using the early age standard curing concrete strength.
The five early methods for estimating concrete strength are that the maintenance difficulty is relatively high and the Ca (OH) is saturated 2 Boiling water, 80 ℃ hot water, 55 ℃ warm water, autoclave curing and the like need special constant temperature equipment, an autoclave and a coagulant, wherein a sealing device is needed for a die with die curing; secondly, the concrete test piece still needs to be molded, the concrete test piece for early stage and the concrete marked to 28d need to be taken from the same disc, and the early strength of the concrete is used for predicting the strength of the concrete 28d and cannot exceed the strength of the concreteThe more this limit; thirdly, the in-use methods are one-to-one models, other factors such as mortar surplus coefficients can be influenced without consideration, and when the raw materials are subjected to small replacement, more accurate prediction cannot be performed. In addition, according to the characteristics of the existing early concrete strength estimating method, the method shows that: according to a concrete strength relation obtained by a certain estimation method, the coefficient is sensitive to the performance of raw materials and is more restricted. Thus, a new method of estimating the concrete 28d is urgently needed.
Disclosure of Invention
Therefore, the invention aims to provide a method for estimating the strength of concrete 28d, which directly adopts 7d mortar to estimate the strength of concrete 28d, does not need high-temperature or autoclave curing, can simplify the operation process, simultaneously avoids waste caused by manufacturing concrete cube test pieces, considers the influence of the surplus coefficient of mortar on the strength of the concrete in an estimation function, has large correlation coefficient of the estimation function, good stability and short required time, has good fitting degree, and can provide quick reference for the concrete quality pre-judgment and the mix ratio adjustment in engineering.
The invention solves the technical problems by the following technical means:
a method for estimating the strength of concrete 28d, comprising the steps of:
(1) Preparing mortar;
(2) Curing the mortar test piece;
(3) Measuring the compressive strength of the mortar test piece 7 d;
(4) Calculating a mortar surplus coefficient according to the mixing ratio and the raw material density data;
(5) Estimated compressive strength of concrete 28 d:
f 28 ＝aγ+bf m,7 -50.5γ 2 -0.03f m,7 2 -271.8；
wherein f 28 -concrete 28d compressive strength (MPa); f (f) m，7 -mortar 7d compressive strength (MPa); gamma-mortar surplus coefficient, a is the coefficient selection range 227.5-229.5, b is the coefficient selection range 3.05-3.15.
Further, when the water-gel ratio is more than or equal to 0.4, the selection range of a is 227-228.5, and the selection range of b is 3.05-3.10; when the water-gel ratio is less than 0.4, the selection range of a is 228.5-229.5, and the selection range of b is 3.10-3.15.
The water-cement ratio is the mass of the cementing material in the mass ratio of water, wherein the mass of the cementing material comprises the total mass of cement, fly ash and mineral powder.
Further, the mortar is prepared after removing coarse aggregates in the concrete.
Further, the concrete operation method for preparing the mortar comprises the following steps:
(1) The temperature in the laboratory should be controlled at 20+/-5 ℃ and the relative humidity is more than 50 percent, and the raw materials for mixing mortar are placed in the laboratory for at least 24 hours;
(2) The sand is sieved by a square hole sieve with the diameter of 9.5mm, the screen residue of a 4.75mm sieve is not more than 10 percent, and the sand materials are uniformly stirred; the cement and the admixture are not allowed to agglomerate, and the cement and the admixture should be sieved by a sieve of 0.9mm before being used;
in addition, the sand should be in a dry state and have a water content of less than 0.2%, and the water content is measured according to the regulations of the current highway engineering aggregate test procedure (JTGE 42).
(3) The material is used in a mass quantity. Weighing precision: cement and admixture, water and admixture are +/-0.5%; sand is + -1%;
during preparation, the mortar stirring pot is cleaned, the pot is kept wet, mortar with the same volume ratio and not less than 30% of the mortar with the same volume ratio is firstly stirred according to the mixing ratio, the inner wall of the stirrer is made to be hung with mortar, and the rest materials are discharged.
(4) Pouring the weighed sand, water, cement, external admixture and the like into a machine in turn, immediately starting the mixer, and stirring for more than 180 seconds. The primary mixing amount is not less than 30% of the capacity of the stirrer, and not more than 70% of the capacity of the stirrer.
Further, the concrete operation method for manufacturing and curing the mortar test piece comprises the following steps:
(1) After coating a thin layer of engine oil or release agent on the inner wall of the test mould, filling mortar into the test mould once, uniformly and spirally inserting and tamping the mortar from outside to inside for 25 times, and allowing a putty knife to insert the mortar along the mould wall for several times to enable the mortar to be 6-8mm higher than the top surface of the test mould in order to prevent holes possibly left after inserting and tamping the mortar with low consistency;
(2) When the surface of the mortar starts to be in a tingling state (the time is about 15-30 min), the mortar of the higher part is scraped off and smoothed along the top surface of the test die;
(3) After the test piece is manufactured, the test piece is stopped for a day and night (24 hours plus or minus 2 hours) under the environment that the temperature is 20 plus or minus 5 ℃ and the humidity is more than 50 percent; when the air temperature is low, the time can be prolonged appropriately, but not more than two days and nights.
And numbering the test pieces and removing the die. After the test piece is removed from the die, the test piece is continuously cured for 7 days under standard curing conditions (the temperature is 20+/-2 ℃ and the relative humidity is more than or equal to 90%), and then the compressive strength is measured.
Further, the dimensions of the test die were 70.7mm×70.7mm.
Further, the mortar 7d has compressive strength f m，7 For the measurement, the measurement was carried out using the test procedure for highway engineering cement and cement concrete (JTG 3420).
Further, the mortar surplus coefficient gamma is a calculated value, and the calculating method of the mortar surplus coefficient is as follows:
wherein, gamma-mortar surplus coefficient; m is m c -mass of cement per unit of concrete (Kg); m is m f Mass (Kg) of admixture a per unit of concrete; m is m k -mass (Kg) of admixture B per unit of concrete; m is m w -mass (Kg) of water per unit of concrete; m is m s -mass (Kg) of fine aggregate in unit concrete; m is m g -mass (Kg) of coarse aggregate in unit concrete; ρ c Density of cement (Kg/m) 3 )；ρ f Density of admixture A (Kg/m) 3 )；ρ k Density of admixture B (Kg/m) 3 )；ρ w Density of water, 1000 (Kg/m) 3 )；ρ s Apparent density of fine aggregate (Kg/m) 3 )；ρ g Apparent density of coarse aggregate (Kg/m) 3 )；ρ′ g Compact bulk Density (Kg/m) of coarse aggregate 3 )。
Furthermore, the method disclosed by the invention is suitable for common concrete, and mainly comprises cement, fly ash, slag powder, coarse and fine aggregates and water, and a proper amount of additive, such as a water reducing agent and the like, can be added for improving certain properties of the concrete. Such as heavy concrete, light concrete, etc., are not suitable for the method of the present invention.
The beneficial effects are that:
1. the method for estimating the 28d strength of the concrete by the 7d mortar strength does not need special equipment, has simple operation process, requires less time, has smaller error between the estimated result and the actual measurement result, has large correlation coefficient and has higher accuracy;
2. the mortar is adopted to estimate the compressive strength of the concrete, so that the experimental process is simplified, and meanwhile, the waste of materials caused by manufacturing a concrete cube test piece is avoided;
3. the influence of the mortar surplus coefficient on the concrete strength is considered in the estimation function, the correlation coefficient of the estimation function is large, the stability is good, the fitting degree is good, and a quick reference can be provided for concrete quality pre-judgment and mix proportion adjustment in engineering.
Drawings
FIG. 1 is a mortar formulated to infer the compressive strength of concrete 28 d;
FIG. 2 is a concrete formulated to measure actual compressive strength;
Detailed Description
The present invention will be described in detail with reference to the following specific examples:
example 1: presumption of concrete 28d Strength
The concrete mixing mass ratios are shown in table 1:
table 1 (Unit: kg)
| Sequence number | Cement and its preparation method | Fly ash | Mineral powder | Fine aggregate | Coarse aggregate | Water and its preparation method | Water reducing agent | Ratio of water to gel |
| 1# | 221 | 48 | 48 | 828 | 1144 | 166 | 3.6 | 0.52 |
| 2# | 285 | 61 | 61 | 711 | 1163 | 171 | 4.9 | 0.42 |
Wherein the cement is ordinary Portland cement with the number of P.O and 42.5 and the density of 3050Kg/m 3 ；
The fine aggregate is the medium sand machine sand in zone II, the fineness modulus is 3.0, and the apparent density is 2780Kg/m 3 ；
The coarse aggregate is 4.75-9.5mm,9.5-19.0mm, and the cobble stone with 19.0mm-31.5mm, and the apparent density is 2960Kg/m 3 Compact bulk density 1780Kg/m 3 The crushed stones with three particle sizes are matched according to proportion;
fly ash density 2640Kg/m 3 ；
The mineral powder is S95 granulated blast furnace slag micropowder with the density of 2910Kg/m 3 ；
The water reducer is a polycarboxylic acid high-performance water reducer, and the water reducing rate is 25.8%;
tap water is used as water, and the density is 1000Kg/m 3 。
The coarse aggregate in the concrete with the two mixing ratios is removed to form a mortar mixing ratio to prepare mortar, and the concrete preparation method comprises the following steps:
(1) The temperature in the laboratory should be controlled at 20+/-5 ℃ and the relative humidity is more than 50 percent, and the raw materials for mixing mortar are placed in the laboratory for at least 24 hours;
(2) The sand is sieved by a square hole sieve with the diameter of 9.5mm, the screen residue of a 4.75mm sieve is not more than 10 percent, and the sand materials are uniformly stirred; the cement and the admixture are not allowed to agglomerate, and the cement and the admixture should be sieved by a sieve of 0.9mm before being used;
in addition, the sand should be in a dry state and have a water content of less than 0.2%, and the water content is measured according to the regulations of the current highway engineering aggregate test procedure (JTG E42).
(3) The material is used in a mass quantity. Weighing precision: cement and admixture, water and admixture are +/-0.5%; sand is + -1%;
during preparation, the mortar stirring pot is cleaned, the pot is kept wet, mortar with the same volume ratio and not less than 30% of the mortar with the same volume ratio is firstly stirred according to the mixing ratio, the inner wall of the stirrer is made to be hung with mortar, and the rest materials are discharged.
(4) Pouring the weighed sand, water, cement, external admixture and the like into a machine in turn, immediately starting the mixer, and stirring for more than 180 seconds. The primary mixing amount is not less than 30% of the capacity of the stirrer, and not more than 70% of the capacity of the stirrer.
The mortar is prepared into a test piece, and the concrete preparation method and the maintenance method are as follows:
(1) Coating a thin layer of engine oil or release agent on the inner wall of a test mould with the dimensions of 70.7mm multiplied by 70.7mm, filling mortar into the test mould for one time, uniformly and spirally tamping the mortar from outside to inside for 25 times, and allowing a putty knife to be inserted along the mould wall for a plurality of times to enable the mortar to be 6-8mm higher than the top surface of the test mould in order to prevent holes possibly left after the low-consistency mortar is tamped;
(2) When the surface of the mortar starts to be in a tingling state (the time is about 15-30 min), the mortar of the higher part is scraped off and smoothed along the top surface of the test die;
(3) After the test piece is manufactured, the test piece is stopped for a day and night (24 hours plus or minus 2 hours) under the environment that the temperature is 20 plus or minus 5 ℃ and the humidity is more than 50 percent; when the air temperature is low, the time can be prolonged appropriately, but not more than two days and nights.
And numbering the test pieces and removing the die. After the test piece is removed from the die, the test piece is continuously cured for 7 days under standard curing conditions (the temperature is 20+/-2 ℃ and the relative humidity is more than or equal to 90%), and then the compressive strength is measured.
The mortar margin coefficient is equal to the mortar volume divided by the coarse aggregate void volume in the concrete, calculated as:
wherein, gamma-mortar surplus coefficient; m is m c -mass of cement per unit of concrete (Kg); m is m f Mass (Kg) of admixture a per unit of concrete; m is m k -mass (Kg) of admixture B per unit of concrete; m is m w -mass (Kg) of water per unit of concrete; m is m s -mass (Kg) of fine aggregate in unit concrete; m is m g -mass (Kg) of coarse aggregate in unit concrete; ρ c Density of cement (Kg/m) 3 )；ρ f Density of admixture A (Kg/m) 3 )；ρ k Density of admixture B (Kg/m) 3 )；ρ w Density of water, 1000 (Kg/m) 3 )；ρ s Apparent density of fine aggregate (Kg/m) 3 )；ρ g Apparent density of coarse aggregate (Kg/m) 3 )；ρ′ g Compact bulk Density (Kg/m) of coarse aggregate 3 )。
According to the formula, the consumption of each raw material is calculated by designing the proportion of the surplus coefficient of the mortar to be 2.03, 2.63 and the components of the mortar.
Mortar forming, curing and compressive strength measurement are carried out according to T0570 specified in Highway engineering Cement and Cement concrete test procedure (JTG 3420); the same materials were used for the mortar and concrete involved in the strength estimation, and the concrete was molded and cured according to T0551 and the compressive strength was measured according to T0553. The measured mortar 7d intensities were respectively: the measured values of the strength of the concrete 28d are respectively as follows: 36.4MPa and 33.3MPa.
And then estimating the compressive strength of the concrete 28d, taking the 1# mortar as an example, wherein when the water-cement ratio of the 1# mortar is 0.52 and both the water-cement ratios are more than or equal to 0.4, the selection range of a is 227-228.5, and the selection range of b is 3.05-3.10.
When a=227, b=3.05, f 28 ＝227γ+3.05f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝33.1MPa，f Push-out /f Real world ＝0.91；
When a=227, b=3.1, f 28 ＝227γ+3.1f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝34.2MPa，f Push-out /f Real world ＝0.94；
When a=228.5, b=3.05, f 28 ＝228.5γ+3.05f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝36.2MPa，f Push-out /f Real world ＝0.99；
When a=228.5, b=3.1, f 28 ＝228.5γ+3.1f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝37.3MPa，f Push-out /f Real world ＝1.02；
From this, it was found that the 28d concrete of # 1 had a predicted strength of f 28 ＝(33.1-37.3)MPa，f Push-out /f Real world = (0.91-1.02), it is relatively accurate to explain the method of estimating the strength of concrete 28d from the 7d mortar strength by the formula of the present invention.
A=227.5 and b=3.08 are chosen for calculation, f 28 ＝228γ+3.1f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculated to obtain the estimated values, the specific values are shown in table 2:
table 2 (a=227.5, b=3.08)
Example 2: estimating the strength of concrete 28d
The concrete mixing mass ratios are shown in table 3:
TABLE 3 Table 3
| Sequence number | Cement and its preparation method | Fly ash | Mineral powder | Fine aggregate | Coarse aggregate | Water and its preparation method | Water reducing agent | Ratio of water to gel |
| 3# | 366 | 46 | 46 | 736 | 1166 | 165 | 6.7 | 0.36 |
| 4# | 480 | 0 | 53 | 680 | 1122 | 162 | 9.1 | 0.30 |
Wherein the relevant parameters of the raw materials are the same as those of the example 1, coarse aggregate in the concrete with the two proportions is removed to prepare mortar, and a mortar test piece is prepared at the same time, and the specific operation method is the same as that of the example 1. The mortar margin coefficient is equal to the mortar volume divided by the coarse aggregate void volume in the concrete, calculated as:
according to the formula, the consumption of each raw material is calculated by designing the proportion of the surplus coefficient of the mortar to be 2.33, 2.63 and the components of the mortar.
Mortar forming, curing and compressive strength measurement are carried out according to T0570 specified in Highway engineering Cement and Cement concrete test procedure (JTG 3420); the same materials were used for the mortar and concrete involved in the strength estimation, and the concrete was molded and cured according to T0551 and the compressive strength was measured according to T0553. The measured mortar 7d intensities were respectively: the strength measured values of the concrete 28d are respectively 34.2MPa and 44.1 MPa: 56.4MPa and 57.5MPa.
Then, the compressive strength of the concrete 28d is estimated, taking 3# mortar as an example, when the water-cement ratio of 3# is 0.36 and is smaller than 0.4, the selection range of a is 228.5-229.5 and the selection range of b is 3.1-3.15.
When a=228.5, b=3.1, f 28 ＝228.5γ+3.1f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝57.4MPa，f Push-out /f Real world ＝1.02；
When a=228.5, b=3.15, f 28 ＝228.5γ+3.15f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝59.1MPa，f Push-out /f Real world ＝1.05；
When a=229.5, b=3.1, f 28 ＝229.5γ+3.1f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝59.7MPa，f Push-out /f Real world ＝1.06；
When a=229.5, b=3.15, f 28 ＝229.5γ+3.15f m,7 -50.5γ 2 -0.03f m,7 2 -271.8, calculating f 28 ＝61.4MPa，f Push-out /f Real world ＝1.09；
From this, it was found that the 28d concrete of 3# had a predicted strength of f 28 ＝(57.4-61.4)Mpa，f Push-out /f Real world = (1.02-1.09), the error is less than 9%, and the method for estimating the strength of the concrete 28d by the 7d mortar strength according to the formula of the invention is accurate, and the accuracy rate is more than 91%.
When a=229, b=3.13, f 28 ＝229γ+3.13f m,7 -50.5γ 2 -0.03f m,7 2 -271.8 calculationTo the estimated values, specific values are shown in table 4:
table 4 (a=229, b=3.13)
The analysis of the data in tables 2 and 4 shows that:
1. the estimated value/measured value is between 0.91 and 1.09, the accuracy is more than 91 percent, and the correlation coefficient of the compressive strength of 28d concrete estimated by adopting 7d mortar compressive strength is large and the accuracy is high.
2. The estimation method can obtain the result by waiting for 7d, remarkably saves time, and can provide quick reference for concrete quality pre-judgment and mix proportion adjustment in engineering.
3. The invention adopts mortar to estimate the compressive strength of the concrete, simplifies the experimental process, reduces the use of special equipment and dies, avoids the waste of manufacturing concrete cube test pieces and saves resources.
4. According to the invention, the influence of the surplus coefficient of mortar on the strength of the concrete is considered, the sensitivity of the obtained estimation formula to raw materials is reduced, and the application range is enlarged on the basis of the existing estimation method.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention, which is intended to be covered by the scope of the claims of the present invention. The technology, shape, and construction parts of the present invention, which are not described in detail, are known in the art.
Claims (3)
1. A method for estimating the strength of concrete 28d, comprising the steps of:
(1) Preparing mortar;
(2) Curing the mortar test piece;
(3) Measuring the compressive strength of the mortar test piece 7 d;
(4) Calculating a mortar surplus coefficient according to the mixing ratio and the raw material density data;
(5) Estimating the compressive strength of the concrete 28 d;
f 28 ＝aγ+bf m,7 -50.5γ 2 -0.03f m,7 2 -271.8；
wherein f 28 -concrete 28d compressive strength (MPa); f (f) m，7 -mortar 7d compressive strength (MPa); gamma-mortar surplus coefficient, a is the coefficient selection range of 227-229.5, b is the coefficient selection range of 3.05-3.15;
the concrete operation method for preparing the mortar comprises the following steps:
(1) Standing the raw materials in a room with the temperature of 15-25 ℃ and the relative humidity of more than 50% for more than 24 hours, wherein the water content of the sand material is lower than 0.2%;
(2) The sand material is sieved by a square hole sieve with 9.5mm, and the cement and the admixture are sieved by a sieve with 0.9 mm;
(3) Keeping the mortar stirring pot wet, stirring the mortar with the same proportion according to the proportion, so that the inner wall of the stirrer is hung with the mortar, and discharging the rest materials;
(4) Sequentially pouring the weighed sand, water, cement and external admixture into a machine, immediately starting the mixer, and obtaining mortar after the mixing is completed, wherein the mixing time is more than 180 seconds;
the concrete operation method for molding and curing the mortar test piece is as follows:
(1) After coating a thin layer of engine oil or release agent on the inner wall of the test mould, filling mortar into the test mould once, and uniformly and spirally tamping the mortar from outside to inside for 25 times;
(2) When the surface of the mortar starts to be in a mottled state, the mortar at the higher part is scraped off and smoothed along the top surface of the test die;
(3) After the test piece is manufactured, the test piece is stopped for a day and night under the environment that the temperature is 15-25 ℃ and the relative humidity is more than 50 percent, and then the test piece is numbered and the die is removed;
(4) After the test piece is removed from the die, continuing to maintain the test piece for 7 days under standard maintenance conditions that the temperature is 18-22 ℃ and the relative humidity is more than or equal to 90%, and then measuring the compressive strength;
the calculation method of the mortar surplus coefficient comprises the following steps:
wherein, gamma-mortar surplus coefficient; m is m c -mass of cement per unit of concrete (Kg); m is m f Mass (Kg) of admixture a per unit of concrete; m is m k -mass (Kg) of admixture B per unit of concrete; m is m w -mass (Kg) of water per unit of concrete; m is m s -mass (Kg) of fine aggregate in unit concrete; m is m g -mass (Kg) of coarse aggregate in unit concrete; ρ c Density of cement (Kg/m) 3 )；ρ f Density of admixture A (Kg/m) 3 )；ρ k Density of admixture B (Kg/m) 3 )；ρ w Density of water, 1000 (Kg/m) 3 )；ρ s Apparent density of fine aggregate (Kg/m) 3 )；ρ g Apparent density of coarse aggregate (Kg/m) 3 )；ρ′ g Compact bulk Density (Kg/m) of coarse aggregate 3 )。
2. The method for estimating a strength of concrete 28d according to claim 1, wherein said mortar 7d has a compressive strength f m，7 For the measurement, the measurement was carried out using the test procedure for highway engineering cement and cement concrete (JTG 3420).
3. A method for estimating the strength of a concrete 28d according to any one of claims 1-2, wherein said method is applied to ordinary concrete.
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