Cement concrete pavement; Construction quality; control
The quality control of cement concrete pavement construction is a systematic project, including raw materials, construction machinery, construction management level, weather change, the proficiency of auxiliary workers, and the operation level of various locomotive drivers. This will directly affect the construction quality. The fundamental measures to ensure and control the construction quality are process control and inspection. Technical Specification for Construction of Highway Cement Concrete Pavement (JTGF30-2003) pays full attention to the quality control and inspection in the construction process, and defines the control and inspection items. Only by strictly following these clear means and methods can the construction quality of cement concrete pavement be realized. This paper first introduces the inspection regulations of raw materials, mixture and pavement construction quality in the code, and then discusses several quality inspection problems in process quality control in combination with actual construction.
First, the quality inspection regulations that must be based on pavement quality control.
(1) Quality inspection of raw materials
The pavement quality of raw materials for cement concrete pavement has a decisive influence on pavement quality, and these inspection items are necessary to control the requirements of raw material quality indicators.
Quality inspection of 1. mixture
The quality of concrete mixture is directly related to the key technical indexes such as flexural strength and smoothness of pavement.
The mixture should be uniform, and it is forbidden to use the mixture with segregation, admixture caking or other uneven phenomena for pavement paving. The allowable deviation of the mixture slump is +/- 10mm, and the mixing slump should be the sum of the slump value most suitable for paving and the slump loss value of transportation at the current temperature.
2. Quality inspection of concrete pavement
(1) The construction unit shall conduct self-inspection on the construction quality of cement concrete pavement at any time. When the construction supervisor finds any abnormal situation, he should increase the detection frequency, find out the reason and deal with it in time. Expressway, the first-class highway should use computer to implement dynamic quality management, and should be carried out in accordance with the provisions of the appendix to the specification.
(2) The mixture produced by each mixing station should not only meet the paving performance of the construction machinery used, but also focus on controlling the uniformity of the mixture and the stability of various quality parameters.
(3) In addition to the inspection items and frequency detection specified in Table 3, the self-inspection requirements of three key quality indexes of concrete pavement, such as flatness, flexural strength and thickness, shall comply with other corresponding regulations.
1) Use a 3m ruler to detect the flatness as a quality control test item in the construction process, and use a flatness meter to check.
Dynamic flatness measurement, as the evaluation basis of engineering quality when the second-class and above highways are completed and accepted, should comply with the relevant provisions of the specification.
2) Random sampling should be taken from the mixture produced by the mixing plant, and the sampling should be based on&; The exam is big&; The standard method specified in "Test Code for Cement Concrete in Highway Engineering" (JTJ053-94) is used to test the flexural and tensile strength of concrete pavement.
3) Before the surface layer is laid, the plate thickness should be strictly controlled according to the baseline or template. The inspection criteria are: the thickness and average thickness of the low side plate of the roadway cross slope should meet the allowable deviation of the design thickness, and the statistical variation coefficient of the plate thickness should meet the design requirements.
4) In the process of paving concrete pavement, the quality inspection and evaluation standards of various technical indexes of pavement should meet the specification requirements.
Second, several practical problems related to quality inspection that affect pavement quality control.
(1) Real quality and certification quality
There are actually two forms of construction quality: real quality and certified quality. The real quality is the quality result produced by various factors that affect the quality in the construction process. Recognized quality is the degree of cognition of real quality through various testing methods. Authentication quality is divided into process authentication quality and result authentication quality. The process certification quality is the tracking and tracing of the real quality production process in the construction process, and the result certification quality is the evaluation of the real quality.
(2) Construction of test section
Concrete pavement construction is still an operation with strong experience, and the results of practice are needed to verify the real situation of theory and parameters. The specification puts forward: "expressway and first-class highways should be paved outside the main pavement." Usually, under the condition of adequate preparation, the success rate of the test section is extremely high, for example, the success rate of the concrete pavement test section in Guangdong Province from 65438 to 0996 to 2000 is over 95%; On the other hand, only laying the experimental section on the main line can reflect the real quality results of the actual engineering environment, while the operation outside the main line is always "simulated" construction, which is difficult to be truly convincing.
(3) Strength
1. On the early strength problem
With the improvement of cement quality, the fineness of cement becomes finer and finer, which actually brings two results: one is the possible increase of drying shrinkage cracks; Second, the strength of concrete is further strengthened. The original intention of developing road cement is to make cement more suitable for cement concrete pavement construction, but our understanding of it is limited to the choice of tetracalcium ferrite, because this active ingredient directly affects the flexural and tensile strength.
In the process of construction, owners, supervisors and construction units should carefully detect the development of early strength from the perspective of experience, and must be alert to the phenomenon of excessive early strength and take necessary measures to control the trend of excessive early strength development.
2. High compressive strength and high performance.
High compressive strength does not mean high bending tensile strength and high durability. When the strength between the panel and the base is not harmonious (the modulus is too large), when the friction between the base and the panel is too large (the constraint is too large), when the brittleness of concrete is increased due to high compressive strength, and when the paving width exceeds 8.00m and the internal constraint is too large, the high compressive strength may lead to the result of reduced durability.
3. Strength test
No matter which method is adopted, the test of flexural and tensile strength of pavement concrete is different from that of pavement. The only difference is that the beam cut on the pavement slab is completely equivalent to the beam under vibration and maintenance conditions. The standard specimen, standard manufacturing method and standard curing conditions proposed in the specification are the benchmark flexural and tensile strength of all concrete materials and are recognized as the benchmark strength values. First of all, ensure that there is no problem with the benchmark strength. The actual strength of the concrete pavement slab is tested according to each lane and kilometer 1 core. The rework order when the bending strength is insufficient can only be finally determined according to the average bending strength of the three core materials from the road surface to each lane.
(4) Incision inspection
Based on the construction quality problems after the implementation of slipform construction technology in some provinces and regions of expressway in recent years, the crack depth is detected and redefined. Slipform pavers need to cut longitudinal and transverse contraction joints after laying a two-lane pavement with a length of more than 8.00m m m. Because there are tie rods when designing longitudinal joints, construction units are often worried about cutting off the tie rods when sawing longitudinal joints, so the cutting depth is not enough (especially for pavers with front tie rods) or the cutting time is too late, which is bound to be detrimental to longitudinal joint crack guidance and panel crack prevention.
(5) Health care quality control
1. At present, the recognized curing method is spraying curing agent and covering the film at the same time. This process is based on the mechanism that water in cement concrete can be completely autotrophic. However, in the actual construction process, the problem of insufficient autotrophic water caused by negligence in maintenance construction often occurs.
2. There is no more convincing test to prove the effectiveness of health care agents in water retention. Because the hydration heat needs to escape, when the curing agent forms a film, the hydration heat will carry a lot of water to break through the cured film and escape, thus destroying its curing effect. More commonly, the curing agent is difficult to form a film on the uneven micro-concrete surface. The results show that the film-forming surface of curing agent is less than 40% when sprayed once, and only 60% ~ 70% when sprayed twice. Therefore, the covering process must not be neglected because of spraying curing agent.
3. At present, there is a double-layer water-retaining and covering method in the maintenance market, that is, after the seam is cut, a porous moisture-retaining and heat-insulating film with interlayer is covered, and the interlayer of the film contains polymer, which can store a large amount of water like a sponge, and is fully replenished by a water wheel &; The exam is big&; After that, a layer of sealing film is covered to achieve the effect of water retention and hydration of concrete. In addition, in the case of saturated humidity, the use of geotextile also makes the water loss slow, as long as the surface of the panel is not white, it also has a good health care effect.
Health care standards do not stipulate mandatory methods, and the specific methods are determined by the construction unit. The general principle of pavement concrete construction and maintenance is: it is required that the concrete surface maintained within the first 7 days cannot be dry and white.
(6) Detection of ground materials
At present, most construction units in China use classified stacking of ground materials such as gravel and river sand, which makes it difficult to detect and determine batches. Therefore, the key to incoming inspection is to determine the batch according to the number of trains, or to confirm it at the production site of the quarry and sand yard. This is a very complicated job. Many construction units often miss the inspection of purchased materials because of trouble or poor management, which makes the inspection frequency stipulated in the specification not guaranteed, which must be paid attention to.
Third, the conclusion
The inspection, acceptance and control of construction quality should run through the whole construction process and strictly control all technological processes and technical links. When using the inspection and acceptance standard indicators required by the specification, we must understand and master the reasons in order to effectively carry out management control.