Lift Rod flexural strength

Time：2021-04-25 View：

Flexural strength refers to the ultimate breaking stress when the unit area of the material bears the bending moment. Also known as bending strength and modulus of rupture.
Ultimate stress when fire-resistant mud material or ceramic materials are damaged by bending load. Expressed by the ratio of the breaking bending moment (Niu · m) to the section resistance moment (cubic centimeters) at the break, in Pa.
The test was conducted on a universal material testing machine. The test piece is a cylinder of (10~16) mm × 120mm or a rectangular cylinder of 10mm × 10mm × 120mm.

 

Concrete calculation
The flexural strength of cement concrete is a 150mm × 150mm × 550mm beam-shaped specimen. After reaching the specified age (28 days) under standard curing conditions, the net span is 450mm, bending and tensile failure under double fulcrum load.

 

Calculation formula
Flexural strength fcf = 1.5fl/(bhh)
Test f-flexural strength (MPa);
F-damage load (N) when subjected to bending resistance;
L -- distance between two pivot points (mm);
B- section width of specimen (mm);
h -- section height of specimen (mm);
The flexural strength can be calculated only when the section occurs between two loading points, otherwise the result of the specimen is invalid.

Influencing factors
Cement Concrete Pavement is directly affected by repeated effects of vehicle load and environmental factors (such as temperature and humidity), so it requires high flexural strength, durability, wear resistance and skid resistance for concrete slab. Among them, flexural strength is an important control index of concrete pavement. Whether its size meets the design requirements will directly affect the overall quality and service life of pavement. To meet the above requirements, to a large extent, it depends on the quality of raw materials, composition of mixture and on-site construction control. Therefore, the road requirements of concrete in the project are analyzed, and the factors affecting its strength are analyzed, so as to select qualified materials, scientifically design and reasonably construct, so as to meet the requirements of various indexes of cement concrete pavement.
The following mainly starts from the aspects of raw material quality, concrete mix proportion design and construction, and briefly analyzes the influencing factors of flexural strength of cement concrete based on the actual situation.

 

Influence of raw material quality on flexural strength of cement concrete pavement
(I) influence of cement quality and dosage on concrete strength
1. The quality of cement will directly affect the strength of concrete and the properties of its mixture. This mainly depends on the technical properties of cement itself, such as calcium rate, shrinkage cracking, abrasion performance, etc. Therefore, pavement cement requires high flexural strength, shrinkage, abrasion resistance, good durability and low elastic modulus.
2. Influence of cement dosage on concrete strength. The dosage is too small to meet the requirements of concrete strength, durability, abrasion resistance, etc.; The dosage is too large, although it can meet the strength requirements, the hydration heat of concrete is large, and the shrinkage is also large, it is easy to crack due to shrinkage. Therefore, the cement dosage should meet the minimum cement dosage requirements, but the maximum cement dosage should also be controlled.
3. Selection of cement varieties and labels. Generally, cement with high strength, small dry shrinkage, good abrasion resistance and durability should be adopted. The selection of its varieties and labels must be comprehensively considered and selected according to factors such as highway grade, construction period, paving time, method and economy. Generally, it is recommended that the cement label: heavy and heavy traffic should not be less than 52.5# and others should not be less than 42.5#.
(Ii) influence of coarse and fine aggregate on concrete strength
1. Influence of coarse aggregate (crushed stone) on concrete strength. Coarse aggregate should be hard, durable and clean, and meet certain grading requirements, so as to ensure that the concrete pavement has sufficient strength, good skid resistance, wear resistance and durability. Therefore, each index should meet the requirements of relevant technical standards, such as needle Flake particle content, mud content, crushing Value Index, particle grading, etc. In particular, the particle grading and grading are good, which not only saves cement but also improves the strength; The grading is unreasonable, which not only wastes cement, but also makes it difficult to meet the strength requirements.
2. Influence of fine aggregate (sand) on concrete strength. Pavement sand requires high density and small specific surface to meet the requirements of workability, hardening strength and durability of fresh concrete, and at the same time achieve the purpose of saving cement. The grading requirements should be considered together with the corresponding coarse aggregate. If the grading is poor, it is difficult to prepare a good mixture. Therefore, fine aggregate should not only be clean, hard and durable, but also meet the specification requirements.
(Iii) influence of water quality and dosage on concrete strength
Water with poor water quality has adverse effects on pavement concrete because it contains chemicals such as oil, acid, salt, organic matter, etc. Therefore, water that does not meet the requirements of relevant indexes should not be used as pavement concrete water.
In addition, the amount of water also has a great influence on the strength of concrete. Under the condition of a certain amount of cement, the amount of water is too large, and the water cement ratio (W/C) is bound to increase, although the construction is convenient, it is difficult to guarantee the concrete strength; The water usage is small, and the concrete workability is poor. Although the strength is easy to guarantee, the construction difficulty increases. Therefore, in the concrete mix design, especially the pavement concrete, the water cement ratio must be controlled.
(Iv) influence of admixture on concrete strength
Proper selection of admixture can improve the technical properties of pavement concrete to a certain extent, such as workability, frost resistance, abrasion resistance and other properties, thus improving the concrete strength. For unused admixture, it should be fully investigated and tested on the spot before deciding whether the selected admixture is applicable. In addition, the requirements of concrete on the preparation process will often be changed after admixture is quoted. Therefore, in actual use, special attention should be paid to the correct dosage and uniform mixing to avoid adverse effects.

 

Influence of composition design on flexural strength of cement concrete pavement
The selection of raw materials is of course important, but whether the mix proportion of pavement concrete can be designed scientifically and reasonably is also an important factor affecting the flexural strength of pavement concrete. As we all know, for the calculation of the thickness of cement concrete pavement slab, the strength evaluation is based on the flexural strength (bending strength), so the concrete mix design should be based on the design flexural strength, durability, wear resistance, workability and other requirements and economic and reasonable principles select raw materials. After testing and necessary adjustment, determine the amount of various constituent materials in the unit volume of concrete. Whether a concrete mix design is reasonable or not depends on the determination of three parameters: water cement ratio, Unit water consumption and sand ratio.
(I) influence of water cement ratio (W/C) on pavement concrete strength
This is a key parameter in the mix proportion design of pavement concrete. Whether it is properly selected or not directly affects the strength of pavement concrete. W/C is too small, poor workability, difficult to control construction; W/C is too large, slump increases, concrete has enough fluidity, convenient construction, but it is difficult to ensure the strength of concrete. Therefore, the selection of W/C must meet "no more than W/Cmax requirements": roads, urban roads and factories and mines are no more than 0.46; Winter construction in frozen areas is no more than 0.45.
(Ii) influence of unit water consumption on pavement concrete strength
Under the condition of a certain water cement ratio, the size of unit water consumption directly affects the workability of concrete, especially slump. When Wo is too large, the amount of cement increases, resulting in waste and slump increases; When Wo is too small, the amount of cement is relatively reduced, which makes it difficult to guarantee the minimum amount of cement (generally, the pavement is not less than 300kg/m3), slump also decreases. These two situations are not conducive to the normal growth of pavement concrete strength. Therefore, the selection of Wo should be moderate.
(Iii) influence of sand ratio on pavement concrete strength
Sand ratio refers to the percentage of fine aggregate (sand) to the total amount of coarse and fine aggregate. The sand ratio is too large, the coarse aggregate is relatively reduced, and it is difficult to play the role of skeleton, affecting the overall strength of concrete pavement; The sand ratio is too small, the coarse aggregate increases correspondingly, and the fine aggregate decreases relatively. Although it can form skeleton, however, it is difficult to make the concrete in a dense state, which is bound to reduce the concrete strength. Therefore, the selection of sand ratio should be appropriate (generally not more than 32% is appropriate for pavement)

 

Influence of construction factors on flexural strength of cement concrete pavement
(I) influence of mixing conditions on concrete strength
It mainly includes mixing equipment, mixing environment, mixing process, etc. The quality of mixed concrete varies with the equipment, environment and technology. Especially mixing time and temperature have great influence on concrete strength. Therefore, the concrete quality should be stable and the strength should be guaranteed. The mixing conditions must be improved, the mixing time must be strictly controlled, and the mixing should be uniform.
(Ii) influence of transportation conditions on concrete strength
The transportation time should not be too long, so as to avoid premature condensation and hardening of concrete and affect the construction. Generally, it can be determined according to cement presetting time and construction climate.
(Iii) during concrete pouring, whether the vibration is sufficient also directly affects the formation of concrete strength.
Therefore, the concrete should be vibrated in time after paving, and strive to be sufficient. In order to improve the vibrating effect, plug-in and flat-plate vibrator can be used to work together to improve the compactness and strength of concrete.
(Iv) influence of construction technology on pavement concrete strength
For example, the vacuum water absorption process can reduce the water cement ratio and improve the bonding strength of the concrete surface before setting and hardening. Therefore, using new technology and new methods to carry out Auxiliary construction can improve the strength of pavement concrete to a certain extent.
(V) the influence of curing conditions on pavement concrete
Including health preservation methods, humidity, temperature, etc. Practice has proved that whether concrete curing is sufficient affects the growth of concrete strength. Therefore, we must pay attention to the curing of pavement concrete. Generally, wet sand and hemp bags can be used for health preservation. Generally, the road surface should be kept moist for not less than 7 days. After that, water should be sprayed properly every day. In this way, the concrete strength of the pavement can be kept increasing continuously.

Compressive strength
Flexural strength: the ultimate breaking stress of the material per unit area under bending moment. Also known as bending strength and modulus of rupture. Whether the particle ratio is reasonable, the size and quantity of pores, whether the organizational structure is uniform and consistent, and whether the combination between particles is firm are important factors that determine the flexural strength of refractory materials. Compressive strength: the load on one-way area when rock mass and soil are damaged by one-way pressure. Simply put, it is a bending limit, and one is the compression limit.