CN110590274A

CN110590274A - Method for preparing concrete by using calcareous sand

Info

Publication number: CN110590274A
Application number: CN201910670737.7A
Authority: CN
Inventors: 姚华彦; 马登辉; 崔绍军; 陈清
Original assignee: Hefei Polytechnic University
Current assignee: Hefei University of Technology; Hefei Polytechnic University
Priority date: 2019-07-24
Filing date: 2019-07-24
Publication date: 2019-12-20

Abstract

The invention relates to the technical field of concrete materials, in particular to a method for preparing concrete by using calcareous sand, which comprises the following components in parts by weight: 665 portions of calcareous sand, 2 to 6 portions of fiber, 385 portions of cement, 1084 portions of stone and 215 portions of water. The invention has the advantages that: the invention can use local materials and improve the economic benefit of engineering construction. Meanwhile, the strength of the calcareous sand is low, so that the strength of the concrete prepared by mixing the calcareous sand as fine aggregate is low, and the strength of the concrete can be obviously improved after basalt fibers are added into the concrete, thereby meeting the requirements of engineering construction.

Description

Method for preparing concrete by using calcareous sand

Technical Field

The invention relates to the technical field of concrete materials, in particular to a method for manufacturing concrete by using calcareous sand.

Background

The calcareous sand comprises calcareous sand and coral sand, and the coral sand is obtained from coral reefs. The hermatypic coral is an intestinal cavity animal in the sea, can absorb calcium dioxide and other calcium substances in seawater, and secretes calcium carbonate as a self outer body protective shell through self digestion and absorption; after the hermatypic coral lives together and multiply, bodies and outer body protective shells of the hermatypic coral are mutually bonded and petrified to form a special rock-soil substance, namely the coral reef. Coral reefs can be divided into two categories: primary coral reefs and secondary coral reefs, in general, coral reefs formed when a body and a calcareous shell of reef-building coral (soft coral wrapped with calcareous skeleton) are left in place are called primary coral reefs, and other coral reefs are called secondary coral reefs.

The coral reef is formed in a sea area with a low tide line of below 50 meters, and under a normal condition, a soil layer of the coral reef can be divided into an upper layer and a lower layer, wherein the upper layer is calcareous sand which is generated by carrying, accumulating and compacting shells and bones of organisms such as reef-building coral and shellfish under an external force; the lower layer is reef limestone, and the cause of the reef limestone is formed by the cementing, petrifaction and other actions of calcareous sand and other biological debris in long geological change.

Airports and highways have been constructed on coral reefs in the early 50's of the 20 th century, but the difference between calcareous sands and land-based sands was not noticed at that time. Since the 20 th century and the 70 th century, in the construction and use processes of coral reef engineering such as oil and gas exploitation, fishery resource development and the like, diseases and accidents of the engineering occur due to the poor characteristics of calcareous sand.

The basic physical and mechanical properties of the calcareous sand summarized at home and abroad are mainly characterized as follows:

1. physical characteristics of particle breakage;

the sand grains with the particle size of more than 2mm and less than 0.5mm of the calcareous sand are found to have regular shapes and relatively smooth surfaces, while the shapes with the particle size of 0.5 mm-2.0 mm are complex and have more edges and corners; the triaxial test of the calcareous sand also finds that the particle size crushing degree is increased along with the increase of the confining pressure, and the particle size of the sample tends to develop in the direction of uniform gradation.

2. The compression characteristics of calcareous sand;

the yield stress of the calcareous sand is smaller than that of the common siliceous sand, and under the same stress condition, the calcareous sand is subjected to sand grain breakage before the common siliceous sand enters a yield state in advance.

3. Research on shear strength and apparent cohesion thereof;

there are three main interpretations of the c-value for the cohesion of calcareous sandy soils: firstly, occlusal force; secondly, capillary action of water in sandy soil; ③ cementation between calcareous sand grains.

4. Dynamic characteristics

The sand body dynamic strength is positively correlated with the average principal stress and negatively correlated with the initial bias stress.

5. Research and analysis of bearing capacity of calcareous sand pile foundation

The broken compressibility of calcareous sand granule is big for calcareous sand pile foundation bearing capacity compares greatly with traditional difference, and Angemeer discovers in on-the-spot stake foundation test that the pile side of actual measurement and pile-end resistance value only have twenty percent of calculated value.

In the construction process of ocean engineering, the traditional quartz sand concrete is difficult to prepare, the land river sand transportation cost is high, and the construction cost and difficulty of the engineering are increased due to the difficulty in material selection. The calcareous sand is widely distributed on the shoal, local materials can be obtained, and the cost can be reduced by mixing the calcareous sand as fine aggregate to prepare the concrete. However, according to the above characteristics, it is an urgent problem to solve how to use calcareous sand as a material to produce a satisfactory concrete.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for preparing concrete by using calcareous sand.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for preparing concrete by using calcareous sand comprises the following components in parts by weight: 665 portions of calcareous sand, 2 to 6 portions of fiber, 385 portions of cement, 1084 portions of stone and 215 portions of water.

Specifically, the fibers are basalt fibers.

Specifically, the basalt fibers are chopped basalt fibers.

Specifically, the chopped basalt fiber has the length of 12mm, the water content of 0.02-0.08, the oil content of 1.48-1.79, the single fiber tensile strength of 2.06 × 103MPa, the tensile strength of 2.51 × 103MPa, the tensile elastic modulus of 80GPa and the elongation at break of 3.28%.

Specifically, the calcareous sand is continuous graded calcareous sand with the diameter of 0-60mm, and the fineness modulus is 2.8.

Specifically, the cement is 42.5-grade ordinary portland cement.

Specifically, the stones are natural crushed stones of continuous gradation.

Specifically, the materials are added into a stirrer in the order of adding stones, sand, cement and basalt fiber, and the stirring is to add solid components for dry stirring for 5 minutes and then add water for wet stirring twice.

Specifically, the fiber had a composition of 4 parts.

The invention has the advantages that: the invention can use local materials and improve the economic benefit of engineering construction. Meanwhile, the strength of the calcareous sand is low, so that the strength of the concrete prepared by mixing the calcareous sand as fine aggregate is low, and the strength of the concrete can be obviously improved after basalt fibers are added into the concrete, thereby meeting the requirements of engineering construction.

Drawings

FIGS. 1-4 show stress-strain curves for different fiber parameters at 0MPa confining pressure, 3MPa confining pressure, 6MPa confining pressure, and 9MPa confining pressure, respectively.

FIG. 5 is a graph showing the respective stages of the curve at a fiber parameter of 4kg/m3 under a confining pressure of 3 MPa.

FIG. 6 is a graph of peak stress versus fiber parameter.

Detailed Description

The concrete of C30 is prepared according to the design rule of concrete mix proportion (JGJ 55-2011).

Through calculation: water-to-glue ratio: 0.56. and the slump constant is 75-90 mm, and the water consumption of the concrete can be calculated as follows: 215kg/m³。

Cement consumption ═ water consumption ÷ water-glue ratio ═ 385kg/m³. The sand rate is 38 percent and is 1m³The concrete (2) had a mass of 2350kg, and the fine aggregate (665 kg) and the coarse aggregate (1084 kg) were calculated. Table 1 shows the amount of calcareous sand concrete material used per cubic meter. With group a as the reference group.

Numbering	Cement/kg	Water/kg	Sand/kg	Pebbles/kg	Fiber/kg
						A	385	215	665	1084	0
B	385	215	665	1084	2
						C	385	215	665	1084	4
D	385	215	665	1084	6

TABLE 1

And (3) preparing a standard sample of 150mm multiplied by 150mm, adding the standard sample into a stirrer according to the charging sequence of the pebbles, the sand, the cement and the basalt fiber in order to uniformly distribute the basalt fiber in the concrete sample, firstly carrying out dry stirring for 5 minutes, and finally carrying out wet stirring by adding water twice. Specifically, the basalt fibers are chopped basalt fibers. The chopped basalt fiber has the length of 12mm, the water content of 0.02-0.08, the oil content of 1.48-1.79 and the single fiber tensile strength of 2.06 multiplied by 10³MPa, tensile strength 2.51X 10³MPa, tensile elastic modulus of 80GPa and elongation at break of 3.28 percent. The calcareous sand is continuous graded calcareous sand with the diameter of 0-60mm, and the fineness modulus is 2.8. The cement is 42.5-grade ordinary portland cement. The stones are natural gravels with continuous gradation.

Uniformly coating a layer of vaseline or other release agents which do not generate chemical reaction with the concrete with moisture in the initial stage on the smooth inner part of the standard test piece mold; then the stirred fluid concrete is filled into about half of the height of a standard mould, a stirring rod is used for spirally and uniformly inserting and tamping from the edge to the middle, each inserting and tamping is to reach the lower end of a test mould, a second layer of concrete is filled after 30 times of inserting and tamping, the inserting and tamping is carried out for 30 times according to the method, then a wooden or rubber hammer is used for knocking the periphery of the mould, so that air bubbles in concrete grout float upwards until the surface of the concrete has laitance and holes on the surface disappear, and finally, a trowel is used for smoothing the surface.

Obtaining a stress-strain curve analysis curve through a triaxial test, allowing a concrete initial test piece to stand for 24h for initial setting, then removing a mold, numbering, transferring the test piece after removing the mold, putting the test piece into a curing room, continuously curing for 28 days under the conditions that the temperature is 20 +/-2 ℃ and the relative humidity is more than 95%, forming four groups of ABCD concrete by using the cured concrete standard test piece, and respectively forming stress-strain curves of different fiber parameters under the confining pressure of 0MPa, the confining pressure of 3MPa, the confining pressure of 6MPa and the confining pressure of 9MPa, as shown in figures 1-4.

In general, the stress-strain curves of the calcareous sand concrete are substantially similar in shape, and the triaxial curve can be divided into four stages (the fiber parameter is 4kg/m under the confining pressure of 3MPa³The curve of time is for example as shown in fig. 5).

a. In the pore compacting stage, pores in the concrete are generated by compacting at the beginning of loading, deformation characteristics are different due to different pores of the sample, the time is short, and an initial nonlinear state is formed.

b. And in the elastic stage, the stress-strain curve of the test piece is basically in a linear state, the stress-strain is in a linear relation, and the test piece can be completely recovered after being unloaded.

c. After entering the unstable failure development stage or the stress softening stage, along with the increase of strain, the stress rises slowly, a large number of cracks are generated, along with the mutual overlapping and combination of the cracks, macroscopic cracks are formed, and the confining pressure can hinder the development of the cracks, so that the effect of the larger confining pressure on the nonlinear deformation of the calcareous sand concrete is more obvious; the stress-strain curve is also compared to the elastic phase, and the inclination angle is gradually reduced until the limit load is reached.

d. And in the post-fracture stage, namely the stage after the test piece reaches the limit load, the test piece still has bearing capacity, the stress is gradually reduced along with the increase of the strain, and when a larger confining pressure exists, the stress is reduced to the residual stress, the stress is not reduced any more, and the deformation is increased continuously.

Generally speaking, under the same confining pressure, when the fiber parameter is from 0kg/m³Continuously increase to 4kg/m³In the process, the peak stress of the calcareous sand concrete rises slowly; while continuing to increase to 6kg/m³The peak stress is reduced, but the reduction amplitude is slow, 6kg/m³The peak stress is still larger than that of the ordinary calcareous sand concrete without basalt fiber. As can be seen from fig. 6, the above phenomenon appears in the relationship curve of the peak stress and the fiber parameter under four kinds of ambient pressure. The optimum result in this embodiment is therefore a fibre parameter of 4kg/m³。

The invention is not to be considered as limited to the specific embodiments shown and described, but is to be understood to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims

1. The method for preparing the concrete by using the calcareous sand is characterized by comprising the following components in parts by weight: 665 portions of calcareous sand, 2 to 6 portions of fiber, 385 portions of cement, 1084 portions of stone and 215 portions of water.

2. The method of claim 1, wherein the fibers are basalt fibers.

3. The method of making concrete using calcareous sand as claimed in claim 2, wherein said basalt fibers are chopped basalt fibers.

4. The method for manufacturing concrete using calcareous sand as claimed in claim 3, wherein said chopped basalt fiber has a length of 12mm, a water content of 0.02 to 0.08, an oil content of 1.48 to 1.79, and a single fiber tensile strength of 2.06 x 10³MPa, tensile strength 2.51X 10³MPa, tensile elastic modulus of 80GPa and elongation at break of 3.28 percent.

5. The method for manufacturing concrete by using calcareous sand as claimed in claim 1, wherein the calcareous sand is a continuous graded calcareous sand with a diameter of 0-60mm and a fineness modulus of 2.8.

6. The method of claim 1, wherein the cement is 42.5 grade Portland cement.

7. The method of claim 1, wherein the stones are natural crushed stones of continuous gradation.

8. The method of claim 1, wherein the solid components are added to the mixer in the order of addition of the gravel, the sand, the cement and the basalt fiber, and the mixing is performed by dry-mixing for 5 minutes and then wet-mixing with water in two portions.

9. The method of claim 1, wherein the fiber comprises 4 parts of the composition.