CN112661456A - Concrete mixing proportion for immersed tube post-cast strip - Google Patents
Concrete mixing proportion for immersed tube post-cast strip Download PDFInfo
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Abstract
The invention relates to a cement concrete preparation technology, in particular to a concrete mixing proportion for a pipe sinking post-cast strip. The concrete comprises the following components, by weight, 375-385 parts of a cementing material; 1760-1780 parts of mineral aggregate and 150-170 parts of water; 32-36 parts of an expanding agent; 8-12 parts of a water reducing agent; the expanding agent comprises 90-93 wt% of magnesium oxide and 1.2-2.2 wt% of calcium oxide. The concrete has the performance meeting the slump of 200 +/-20 mm, the expansion of 450 +/-50 mm, the initial setting time of more than or equal to 10h, the final setting time of more than or equal to 12h, the 28d compressive strength of more than or equal to C45 and the volume weight of 2360(-10 to +10) kg/m3The 28d impervious rating is not less than P10, the 28d drying shrinkage is less than 320 mu epsilon, and the limited expansion rate is not less than 0.015 percent after curing in water for 28 days.
Description
Technical Field
The invention relates to a cement concrete preparation technology, in particular to a concrete mixing proportion for a pipe sinking post-cast strip.
Background
The traditional method for controlling cracks by setting the permanent structural joints in engineering construction is complex in construction process, difficult in seepage prevention and leakage prevention, high in cost and high in later maintenance cost, and the vertical face effect of a building is influenced. In order to prevent harmful cracks possibly generated by uneven temperature and shrinkage of cast-in-place reinforced concrete pipe sections, temporary construction joints are reserved at corresponding positions according to design or construction specification requirements, the construction joints are built to shrink internally, the construction joint concrete is poured and tamped after a plurality of times, and the positions where the construction joints are arranged are called as pipe sinking post-pouring zones.
The car slope tunnel immersed tube concrete adopts the full-section pouring and the pouring process of arranging the post-pouring belt. The design adopts integral pipe joints, and although the structural rigidity is higher, the risk of concrete cracking is also higher. Under the condition of higher structural rigidity, in order to ensure the engineering quality and the service life of the immersed tube tunnel, the cracking sensitivity analysis of the immersed tube concrete structure is required. The concrete poured on the full section mainly comprises water, cement, fly ash, sand, stones and a water reducing agent according to the mixing ratio. The post-cast strip concrete differs from full-section concrete mainly in the expanding agent, so the selection of the expanding agent material is a key factor among factors influencing the cracking of the post-cast strip concrete.
For example, in chinese patent CN111470821A, a high performance fiber concrete and its preparation method, the adopted composite expanding agent is compounded by calcium oxide, magnesium oxide and ettringite according to the weight ratio of 2:2: 1.
However, the concrete prepared by the composite expanding agent in the proportion still has obvious cracks in the construction process, and the composite expanding agent cannot meet the performance index of the mixing ratio of the concrete for the immersed tube post-cast strip.
Disclosure of Invention
The invention aims to: aiming at the problems that in the prior art, in tunnel immersed tube engineering, the integral tube joint has high structural rigidity and a large risk of concrete cracking and the existing composite expanding agent cannot meet the performance index of the concrete mixing ratio of a post-cast strip, the concrete mixing ratio for the immersed tube post-cast strip is provided, and the mixing ratio improves the shrinkage performance of concrete and reduces concrete cracks by controlling the proportion of calcium oxide and magnesium oxide in the composite expanding agent and the proportion of the expanding agent and a water reducing agent.
In the invention, the concrete for the immersed tube post-cast strip has the following performance indexes of mixing ratio:
slump of 200 +/-20 mm, expansion of 450 +/-50 mm, initial setting time of not less than 10h, final setting time of not less than 12h, 28d compressive strength of not less than C45 and volume weight of 2360(-10 to +10) kg/m3The 28d impervious rating is not less than P10, the 28d drying shrinkage is less than 320 mu epsilon, the restriction expansion rate is not less than 0.015 percent after 28 days of water curing, and the concrete has good appearance.
The type of the expanding agent is calcium oxide expanding agent, magnesium oxide expanding agent or calcium oxide and magnesium oxide composite expanding agent. The hydration reaction rate of the calcium oxide expanding agent is too high, so that the early shrinkage of the concrete is mainly compensated, and the hydration reaction rate of the magnesium oxide expanding agent is relatively low, so that the calcium oxide expanding agent mainly has a compensation effect on the later shrinkage of the concrete. Therefore, the cracking problem of the post-cast strip concrete can be greatly improved by adopting the calcium-magnesium compound type expanding agent to prepare the post-cast strip micro-expansion concrete and enhancing the maintenance of the post-cast strip concrete. However, in practical effect, the composite expanding agent in the prior art cannot meet the design requirement, and still has more cracks.
For this reason, the inventors have conducted experiments on various swelling agents currently on the market. The existing two types of expanding agents mainly comprise calcium sulphoaluminate expanding agents and magnesium oxide expanding agents, and experiments on the expanding agents in the market show that the calcium sulphoaluminate expanding agents cannot meet the strength requirement of C45, part of the magnesium oxide expanding agents cannot meet the strength requirement of C45, and part of the magnesium oxide expanding agents can meet the strength requirement of C45. In view of the results, the inventor analyzes and verifies the components of the magnesia expanding agent, and finds that the expanding agent which can meet the performance requirements has the weight percentage of magnesia of 90-93 percent; the weight percentage of calcium oxide in the expanding agent is 1.2-2.2%.
Therefore, the concrete can meet the requirements that the concrete comprises the following components in parts by weight, 375-385 parts of cementing materials; 1760-1780 parts of mineral aggregate and 150-170 parts of water; 32-36 parts of an expanding agent; 8-12 parts of a water reducing agent;
the weight percentage of the magnesium oxide in the expanding agent is 90-93%; the weight percentage of calcium oxide in the expanding agent is 1.2-2.2%.
Preferably, 386 parts of cementing material; 1770 parts of mineral aggregate and 160 parts of water; 34 parts of an expanding agent; 10 parts of a water reducing agent;
preferably, the weight percentage of the magnesium oxide in the expanding agent is 91.5%; the weight percentage of calcium oxide in the expanding agent is 1.5%.
The gel material comprises the following components, by weight, 295-305 parts of cement and 80-88 parts of fly ash; the mineral aggregate comprises, by weight, 670-690 parts of sand and 1060-1130 parts of stones.
Preferably, the gel material comprises the following components in parts by weight, 302 parts of cement, 84 parts of fly ash; the mineral aggregate comprises, by weight, 680 parts of sand and 1090 parts of stones.
In view of the above experimental results, the expanding agent has a large influence on the performance, and the inventor has also performed an experiment on another additive, namely, the water reducing agent, when performing an experiment on the mixing ratio. The water reducing agent commonly used at present is a retarding polycarboxylic acid water reducing agent. Experiments on the water reducing agent show that the compressive strength of the water reducing agent product with the total alkali weight ratio of less than 1 percent is obviously higher than that of the water reducing agent with higher total alkali weight.
Therefore, the water reducing agent is a retarding polycarboxylate water reducing agent. The total alkali content in the water reducing agent is less than 1%.
The preparation method of the concrete comprises the following steps,
s1: uniformly stirring and mixing the gel material, the mineral aggregate and the expanding agent according to the proportion, and then adding water and the water reducing agent to obtain water cement;
s2: and (4) putting the cement mortar obtained in the step (S1) into a mold, hardening and forming, and curing for 7-28 days at the temperature of 20-40 ℃ and the relative humidity of 40% -80%.
Through the research on the influence of temperature on the free expansion value and the limited expansion value of a magnesia expansive agent neat paste test piece, the magnesia expansive agent is relatively sensitive to the temperature range of 40-80 ℃ and is not sensitive to the temperature range of 20-40 ℃. Therefore, the maintenance temperature is controlled within the range of 20-40 ℃, and the performance is better.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. according to the concrete for the immersed tube post-cast strip, the proportion of magnesium oxide to calcium oxide is 90-95: 1-2, so that concrete cracks are obviously reduced, the performance of the concrete meets the requirements of 200 +/-20 mm of slump, 450 +/-50 mm of expansion, 10h or more of initial setting time, 12h or more of final setting time, 28d compressive strength or more than C45 and 2360(-10 to +10) kg/m of volume weight3The 28d impervious rating is not less than P10, the 28d drying shrinkage is less than 320 mu epsilon, and the limited expansion rate is not less than 0.015 percent after curing in water for 28 days.
2. The concrete for the immersed tube post-cast strip is maintained for 7-28 days under the conditions of 20-40 ℃ and 40-80% of relative humidity by controlling the oxidation condition during maintenance, so that the performance of the concrete is ensured, and cracks are avoided.
Drawings
FIG. 1 is a schematic structural diagram of a temperature control test result of a simulation experiment of post-cast strip concrete according to the present invention.
FIG. 2 is a schematic structural diagram of the temperature control test result of another simulation experiment of the post-cast strip concrete of the present invention.
FIG. 3 is a graph showing the effect of temperature on the free expansion value of a test piece of a neat paste of a magnesium oxide expanding agent.
FIG. 4 is a graph showing the effect of temperature on the free expansion value of a test piece of the magnesia expansive agent mortar.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
The raw materials are as follows:
(1) cement: P.II 42.5R, Huarun Cement (Pinnan) Ltd., specific surface area 375m2Per kg, initial setting time 139min, final setting time 209min, 3d compressive strength 33.2MPa, 28d compressive strength 53.2 MPa;
(2) fly ash: guangzhou Yuhong fly ash comprehensive development company, F class II fly ash, sieve residue of 45 μm square hole sieve 26.2%, water requirement ratio 100%;
(3) slag powder; the Anshan iron and steel group company Spanish mackerel colony division company, S95 slag powder, the specific surface area of 415m2/kg, the 7-day activity index of 78%, the 28-day activity index of 96% and the fluidity ratio of 108%.
(4) Sand: dongjiang river sand, apparent density 2610kg/m3Bulk density 1520kg/m3Compact density 1620kg/m3The bulk porosity is 42%, the compact porosity is 38%, the mud content is 0.5%, the mud block content is 0.1%, the shell content is 0.1%, and the fineness modulus is 2.6.
(5) Stone: small crushed stone, 5-10 mm, Whitman's Po gold stone field, apparent density 2640kg/m3The mud content is 0.8 percent, and the mud block content is 0.1 percent; large broken stone, 5-25 mm, Whitman's palo gold stone field, apparent density 2640g/m3Bulk density 1440g/m3Compact density 1530g/m3The bulk porosity was 45%, the compact porosity was 42%, the sludge content was 0.4%, the clod content was 0.0%, the needle-like content was 4%, and the crushing index was 9.2%.
(6) Additive: the retarding superplasticizer is prepared from Liuhe novel building materials Co., Ltd, Guangzhou city, and has a solid content of 12.6% and a water reducing rate of 20.4%.
(7) The expanding agent, namely a Subot MgO expanding agent (M type), the content of magnesium oxide is 92.4 percent, the active reaction time is 110s, the content of free calcium oxide is 1.6 percent, the fineness (the screen residue of a square-hole sieve with the size of 80 mu M) is 2.2 percent, the limited expansion rate of 7d in water at 20 ℃ is 0.015 percent, the limited expansion rate of 7d in water at 40 ℃ is 0.031 percent, the compressive strength of 7d is 23.6MPa, and the compressive strength of 28d is 44.9 MPa;
water, 160, cement 302, fly ash 84, water reducing agent 10, sand 712, small broken stone 214, large broken stone 857 and expanding agent 34.
The slump is 190mm, the expansion is 450mm, the setting time is 12-14 hours, the 28d compressive strength is 52.1MPa, and the bulk density is 2360kg/m3The expansion rate is limited to be 0.01 percent in water with the temperature of 40 ℃ and 0.028 percent in water with the temperature of 40 ℃. Meets the requirements.
According to design paper specifications GB50108-2008 'underground engineering waterproof technical specification' and 4.4.13, the concrete mold-entering temperature is controlled to be 5-30 ℃ according to GB50496-2018 'large-volume concrete construction standard' 5.1.7. JTS202-2-2011 Water transport engineering concrete quality control Standard 6.4.11, the temperature of concrete mixture transported to a pouring site is not higher than 35 ℃ at most; the minimum temperature is not preferably lower than 5 ℃. The pouring of the mass concrete is carried out reasonably in a sectional and layered manner, so that the concrete rises uniformly along the height; pouring is carried out at a time interval with low outdoor air temperature, and the pouring temperature of the concrete is not more than 28 ℃. According to the summary suggestion of the cracking risk assessment report of the large-volume concrete of the immersed tube, the mold-entering temperature can be relaxed from 28 ℃ which is not required to exceed the design rule to 30 ℃. The temperature of the pre-cast and post-cast belt-in mould is averagely controlled within the range of 31-32 ℃.
The results of the temperature control tests of the two experimental sections are shown in fig. 1 and fig. 2.
The effect of temperature on the free expansion and limiting expansion values of the magnesia expansive agent neat paste test pieces is shown in fig. 3 and 4.
Example 2
The expanding agent adopts Wuhan three-source MgO expanding agent (M type), the content of magnesium oxide is 86.5 percent, the active reaction time is 112s, the fineness (the screen residue of a square-hole sieve with 80 mu M) is 1.6 percent, the 7d limited expansion rate in water with the temperature of 20 ℃ is 0.015 percent, the 7d limited expansion rate in water with the temperature of 40 ℃ is 0.062 percent, the 7d compressive strength is 38.8MPa, and the 28d compressive strength is 52.8 MPa.
Water, 160, cement 302, fly ash 84, water reducing agent 5.88, sand 677, small broken stone 221, large broken stone 883 and expanding agent 34.
Slump of 200mm, expansion of 475mm, setting time of 12-14 hours, 28d compressive strength of 54.9MPa and bulk weight of 2360kg/m3The limited expansion rate is 0.007% at 7d in water at 40 ℃ and 0.026% at 28d in water at 40 ℃. Meets the requirements.
Example 3
The swelling agent is Subot HME-V swelling agent (containing magnesium swelling agent) with fineness of 325m2The expansion rate of 7d in water is 0.059 percent, the expansion rate of 21d in air is-0.012 percent, the compressive strength of 7d is 23.9MPa, and the compressive strength of 28d is 43.8 MPa;
water, 160, cement 302, fly ash 84, water reducing agent 5.88, sand 677, small broken stone 221, large broken stone 883 and expanding agent 34.
Slump of 200mm, expansion of 475mm, setting time of 18-20 hours, 28d compressive strength of 53.5MPa and bulk weight of 2360kg/m3The expansion limiting rate is 0.006% in water with 7d at 40 ℃ and 0.023% in water with 28d at 40 ℃. Meets the requirements.
Test example 1
Material screening
In order to better analyze the influence of the expanding agent and the water reducing agent on the performance of the concrete, the performance of other materials is firstly tested and analyzed, and the material screening aims to eliminate the influence of other material factors.
1.1 Cement
The cement products of various manufacturers are subjected to performance tests, clinker of P.II 42.5R and P. O42.5R cement and finished cement products are selected for detection, and the results are shown in tables 1-1 and 1-2.
TABLE 1-1 Cement chemistry Performance test results
TABLE 1-2 Cement physical Properties test results
As can be seen from the results of the chemical analyses of the cements in Table 1-1, the results of the chemical property tests of the cements were all acceptable. However, the alkali content of Huarun cement and Zhujiang cement is lower and is less than 0.6%, while the alkali content of conch cement and stone well cement exceeds 0.6%. In addition, the chloride ion content of Huarun cement and Zhujiang cement is lower than that of sea snail cement and stone well cement.
As can be seen from the results of the physical analyses of the cements in tables 1-2, the results of the physical property tests of the cements were all acceptable. The water consumption for the standard consistency of each cement is not very different. The specific surface area of the Zhujiang cement is centered, the setting time is slightly short, and the strength of the 3d cement and the 28d cement is centered; the Huarun cement has the smallest specific surface area, the setting time is in the middle, and the 3d and 28d cements have higher strength.
The comprehensive comparison shows that the Huarun P. II42.5R cement has the best performance, and the Zhujiang P. II42.5R cement is the second cement.
1.2 fly ash
The performance of the fly ash used by each manufacturer was tested and the results are shown in tables 1-3.
Tables 1-3 fly ash Performance test results
As can be seen from the test results in tables 1-3, the fly ash used in each mixing plant was judged to be acceptable according to the evaluation of fly ash used in cement and concrete (GB/T1596-2017). All the fly ashes are II-grade fly ashes. As the supply amount of the I-grade fly ash in the bead triangle area is small, the II-grade fly ash can be used under the condition of meeting the construction requirement.
Wherein, the water quantity ratio and the ignition loss of Guangzhou macro fly ash are in the range of I-class fly ash, and the fineness is in the range of II-class fly ash. The ignition loss of the developed environment-friendly fly ash is in the range of I-class fly ash, and the water demand ratio and the fineness are in the range of II-class fly ash. The fineness, the water demand ratio, the ignition loss and the like of the fly ash in the building-dragon trade and sand-corner power plants are larger and are in the range of II-grade fly ash.
Comprehensively, the Guangzhou Honghou II-grade fly ash has the best quality, and then is the II-grade fly ash for developing environment-friendly building materials.
1.3 Fine aggregate
The performance of the sand used by each manufacturer was examined and the results are shown in tables 1-4 to tables 1-6.
TABLE 1-4 Sand Performance test results
TABLE 1-5 Sand Performance test results (II)
TABLE 1-6 particle size distribution of sands
As can be seen from the table, the Dongjiang river sand, the Wuzhou river sand, the Xijiang river sand and the Ganjiang river sand all meet the standard requirements of the Sand for construction (GB/T14684-. Wherein, the sand of the Dongjiang river has low mud content, no mud block, good gradation (basically in the median of the cumulative screening curve of the sand in the 2 areas), lower mica and sulfide content, better sand quality than other manufacturers, and is coarse sand in the I-type 2 area; the sand grade of the Xijiang river is better, the mud content and the mud block content are lower, the quality is slightly inferior to that of the Dongjiang river sand, and the sand is coarse sand in a II-type 2 area.
In general, the sand from the east river has the best quality, and the sand from the west river is the sand.
1.4 coarse aggregate
The performance of the crushed stones used by each manufacturer was measured, and the results are shown in tables 1-7 to 1-9.
Tables 1-7 crushed stone Performance test results
Table 1-8 crushed stone grading test results
Table 1-9 crushed stone grading test results
As can be seen from the table, each crushed stone sample index meets the specification requirements. The macadam of Poroco Huizhou has better quality than macadams of Guangdong Yunfu, Zengcheng Taizhen and Huizhou due to low needle-shaped content, low crushing index, low mud content and mud block content. From the grading test results of tables 1-8 and tables 1-9, the rubble grading of borro, huizhou is good and meets the requirement of continuous grading. And secondly, the crushed stone floated in the Guangdong cloud is lower in flake content, crushing index, mud content and mud block content than those of Zengcheng Taizhen and Huizhou Shuangdong, and the gradation can meet the requirement of 5-25 mm continuous gradation, and only the particles are more in the range of 10-16 mm.
In comprehensive comparison, the crushed stone of the booby stone field in huizhou is the best in quality, and the crushed stone of the Guangdong cloud pumice is the second crushed stone.
Test example 2
Effect of expansion Agents on concrete Performance
The expansion agent for concrete is detected by the limited expansion rate according to the national standard concrete expansion agent (GB/T23439-2017) and the magnesium oxide expansion agent for concrete (CBMF19-2017), and the results are shown in tables 2-1 and 2-2.
TABLE 2-1 test results of calcium sulphoaluminate swelling agent performance
TABLE 2-2 examination of the properties of magnesium oxide based expanders
As can be seen from tables 12 and 13, the respective swelling agents satisfy the specification in terms of swelling properties. Wherein, when the mortar mixed with the UEA expanding agent is in the air for 21 days, the mortar is already shrunk; and the mortar of HME-V (containing the magnesium expanding agent), the three-source magnesium oxide expanding agent and the Subot magnesium oxide expanding agent which are mixed with the magnesium expanding agent continuously expands under the water curing condition. According to the continuous test results, the mortar doped with the magnesium expanding agent still has slight expansion at 120 days, and the drying shrinkage of the concrete is basically stable after 90 days. Therefore, the magnesium expanding agent is superior to the UEA expanding agent in terms of controlling cracks of concrete for the immersed tube post-cast strip.
Concrete mix proportion design
The expansive agent in the step 5 and other raw materials in the example 1 are adopted, and the concrete mixing proportion for the post-cast strip of the immersed tube is preliminarily designed according to the performance requirements of the immersed tube concrete and by referring to relevant standards and the concrete mixing proportion of the post-cast strip, and is shown in tables 2-3.
The strength grade of the post-cast strip of the immersed tube is 28 days C45, concrete is prepared by HME-V (containing magnesium) expanding agent, 120s magnesium oxide expanding agent, UEA expanding agent and the like respectively, and the working performance, the compressive strength, the limited expansion rate and the like of the hardened concrete are tested.
TABLE 2-3 concrete for post-cast strip of immersed tube
The working performance of the post-cast strip concrete mixture is shown in tables 2-4
TABLE 2-4 concrete mixture Performance test
The results show that the volume weight of each fresh concrete, except for HJD5, meets the design requirements. The concrete mixture workability of HJD1, HJD3 and HJD4 is good, and the slump is 190-205 mm when the concrete mixture is taken out of the mixer. In addition, the setting time of HJD1 is 18-20 h, and the setting time of HJD3 and HJD4 is 12-14 h respectively. Various performances of the mixtures of HJD1, HJD3 and HJD4 meet the design and construction requirements.
The compressive strength of the concrete of the post-cast strip doped with the expanding agent is shown in tables 2 to 5.
TABLE 2-5 mechanical Property test results of concrete for immersed tube post-cast strip
The test results show that:
(1) the HJD6 and HJD5 have lower mixing ratio 28d strength and the strength level does not reach C45;
the strength of the concrete 28d of HJD1, HJD3 and DJD4 is 53.5MPa, 53.2MPa, 52.1MPa and 54.9MPa, and the strength grade reaches C45 in 28 days. The strength of the product can meet the requirement in 56 days.
(2) The concrete has the advantages of larger usage amount of the cementing materials and lower mixing proportion of HJD2, and the compressive strength of the concrete at each age is equivalent to that of HJD 1. Therefore, the post-cast strip concrete adopts the dosage of the cementing material of 420kg/m3 and the water-cement ratio of 0.38 can meet the requirement of the strength of the post-cast strip concrete.
The results of the limited expansion test of the post-cast strip concrete for each group are shown in tables 2-6 and tables 2-7.
TABLE 2-6 limit expansion ratio test of concrete (magnesium expansive agent) for immersed tube post-cast strip
Table 2-7 concrete for immersed tube post-cast strip (UEA expansion agent) limited expansion rate test
As can be seen from the data in tables 2-6 and tables 2-7, the limited expansion ratio of each group of concrete meets the specification requirements. The concrete setting time of HJD1 is longer, the strength of HJD6 is lower, and the limited expansion rate of HJD4 and HJD5 is smaller.
The HJD1 and DJD3 solutions are better when combined with collapse/expansion, compressive strength and limited expansion.
Test example 3
The components and properties of the four magnesium oxide-based expansion agents referred to in test example 2 were further tested, and the test results were as follows:
1. a Subot HME-V expander (magnesium-containing expander),
the content of magnesium oxide is 91.1 percent, the active reaction time is 120s, and the content of free calcium oxide is 1.6 percent;
2. a Subot MgO bulking agent (type M),
the content of magnesium oxide is 91.1 percent, the active reaction time is 110s, and the content of free calcium oxide is 1.6 percent;
3. wuhan three-source MgO expanding agent (M type),
the content of magnesium oxide is 90.5 percent, the active reaction time is 112s, and the content of free calcium oxide is 1.5 percent;
4. henan Bolang MgO expanding agent (M type),
the content of magnesium oxide is 89.2 percent, the active reaction time is 150s, and the content of free calcium oxide is 1.5 percent;
according to the results, the proportion of the magnesium oxide and the calcium oxide is preliminarily judged to have certain influence on the performance of the concrete.
Concrete was prepared and tested for mechanical properties and limiting expansion ratio as shown in tables 3-2 and 3-3 by adding analytically pure magnesium oxide or calcium oxide based formulation of HJD3 in Experimental example 2 but with the same total amount of expanding agent as shown in Table 3-1.
TABLE 3-1 design ratios for the impact of the ratio of magnesium oxide to calcium oxide
TABLE 3-2 Effect of magnesium oxide and calcium oxide ratios on concrete mechanical Properties
TABLE 3-3 Effect of magnesium oxide to calcium oxide ratio on limiting expansion ratio
From experiments 1-4, it can be seen that the compressive strength properties are substantially stable when the weight percentage of magnesium oxide is in the range of 90% to 93% and the weight percentage of calcium oxide is in the range of 1.2% to 2.2% without changing other components. The limiting expansion rate increases with increasing proportion of calcium oxide. When the proportion of calcium oxide is less than 1.2%, the expansion rate is restricted to approach the limit of 0.015%.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (8)
1. The concrete for the post-cast strip of the immersed tube is characterized by comprising the following components in parts by weight, 375-385 parts of cementing materials; 1760-1780 parts of mineral aggregate and 150-170 parts of water; 32-36 parts of an expanding agent; 8-12 parts of a water reducing agent;
the weight percentage of the magnesium oxide in the expanding agent is 90-93%; the weight percentage of calcium oxide in the expanding agent is 1.2-2.2%.
2. The concrete for the post-cast strip of the immersed tube according to claim 1, wherein the weight percentage of magnesium oxide in the expanding agent is 91.5%; the weight percentage of calcium oxide in the expanding agent is 1.5%.
3. The concrete for the post-cast strip of the immersed tube as claimed in claim 1, wherein the gel material comprises the following components, by weight, 295-305 parts of cement and 80-88 parts of fly ash.
4. The concrete for the post-cast strip of the immersed tube as claimed in claim 1, wherein the mineral aggregate comprises 670 to 690 parts by weight of sand and 1060 to 1130 parts by weight of stones.
5. The concrete for the post-cast strip of the immersed tube according to claim 1, wherein the water reducing agent is a retarding polycarboxylic acid water reducing agent.
6. The concrete for the post-cast strip of the immersed tube according to claim 1, wherein the total alkali amount in the water reducing agent is less than 1%.
7. The concrete for a post-cast strip of a sinking pipe according to claim 1, wherein the properties are as follows,
slump of 200 +/-20 mm, expansion of 450 +/-50 mm, initial setting time of more than or equal to 10h, final setting time of more than or equal to 12h, 28d compressive strength of more than or equal to C45 and volume weight of 2360(-10 to +10) kg/m3The 28d impervious rating is not less than P10, the 28d drying shrinkage is less than 320 mu epsilon, and the limited expansion rate is not less than 0.015 percent after curing in water for 28 days.
8. A method for the production of concrete according to any one of claims 1 to 7, comprising the steps of,
s1: uniformly stirring and mixing the gel material, the mineral aggregate and the expanding agent according to the proportion, and then adding water and the water reducing agent to obtain water cement;
s2: and (4) putting the cement mortar obtained in the step (S1) into a mold, hardening and forming, and curing for 7-28 days at the temperature of 20-40 ℃ and the relative humidity of 40% -80%.
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| CN107572957A (en) * | 2017-09-15 | 2018-01-12 | 广西路桥工程集团有限公司 | A kind of self-compaction non-shrinking steel pipe concrete |
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