1, the key to the detection of common highway materials.
Test detection is an effective means to detect the quality of highway engineering. The purpose of this work is to judge whether the engineering quality or product quality meets the current relevant technical standards through the detection of a product or project. The detection of common materials in road engineering is also an important part of engineering quality management, and it is also the main link of highway engineering quality control evaluation and acceptance.
(1) Through necessary tests, the quality of various raw materials, finished products and semi-finished products can be scientifically evaluated. With this set of effective and scientific testing methods, any material can be tested to evaluate whether its products are qualified or not. This is very important for rational application of materials and improvement of engineering quality.
(2) Through the test, it is beneficial to popularize new technologies, new processes and new materials. A timely and effective test of a new material, new technology and new technology can identify its feasibility, applicability, effectiveness and advancement, thus accumulating experience and lessons for engineering construction. This will play a positive role in promoting the progress of construction technology and improving the progress and quality of the project.
(3) The test can reasonably control and scientifically evaluate the construction quality. Engineering quality includes quality control during construction and evaluation and acceptance after completion, and test detection is undoubtedly a scientific and effective method and means.
(4) Through experiments, we can make full use of locally produced materials, which is convenient for local materials. For example, there are sand and gravel, fillers and so on. In the construction site, it can be determined whether these materials meet the requirements of construction technical specifications through experimental testing, which is convenient for local materials and reduces the project cost.
2, highway commonly used materials performance and test items
The basic properties of highway materials can be divided into physical properties (such as density, bulk density, porosity, compactness, water absorption, frost resistance, thermal conductivity, etc. ), chemical properties (chemical stability, etc. ) and mechanical properties (such as strength, hardness, elasticity and plasticity, etc. ).
To build an expressway, we must first close the good materials. Qualified and high-quality materials, combined with mature technology and skilled skills, can ensure the quality of highway engineering. Used for steel, cement, fly ash, sand, gravel or pebbles, concrete admixture, petroleum asphalt, backfill soil, etc. Commonly used in highway construction, we must first know the items that materials must be inspected, so as to make an accurate judgment on whether the materials are qualified or not.
(1) Cement: mortar strength, stability, initial setting time, final setting time and, if necessary, mortar fluidity.
(2) Sand: sieve analysis, silt content, silt content, apparent density, compactness and bulk density are carried out when necessary.
(3) Gravel or pebble: sieve analysis, silt content, fragmentation, needle content, crushing index value, and if necessary, bulk density and apparent density.
(4) Fly ash: fineness, loss on ignition and water demand ratio.
(5) Concrete admixture (water reducing agent): solid content, water reducing rate, bleeding rate, compressive strength ratio, steel bar corrosion, air content if necessary, setting time and slump loss.
(6) Backfill material (improved expansive soil): liquid plastic limit test (liquid limit, plastic limit, plastic finger), compacted resilience modulus (maximum dry density, optimum water content), CBR test (CBR, water absorption, expansion rate, free expansion rate, total expansion and contraction rate).
(7) Steel raw materials: tensile test, cold bending test and repeated bending test.
(8) Reinforcement welding (lap welding): tensile test.
3. Common detection methods
(1) raw material inspection of steel bars shall be based on the same factory, the same heat number, the same specification, the same delivery status and the same entry time, and every 20t shall be an acceptance batch. If one item does not meet the technical requirements of steel bars, double specimens (samples) shall be taken for re-inspection; If the other item is unqualified, the acceptance reinforcement shall be judged as unqualified. Unqualified steel bars shall not be used, and a treatment report shall be made to prevent them from being mixed with other batches.
(2) The inspection of bagged cement should be based on the cement from the same cement plant, the same label, the same production time and the same entry date, with 50t as an acceptance batch.
(3) The detection of bulk cement shall be based on the cement of the same variety and label produced by the same cement factory at the same time, and the cement with the same factory number shall enter the factory (field) as a batch at a time, but the total amount of each batch shall not exceed 50t. At the same time, we should also pay attention to the validity period of cement (generally 3 months for cement and 0/month for portland cement/kloc). Re-inspection must be carried out after the expiration of the validity period, and the time of two cement tests adjacent to continuous construction projects shall not exceed its validity period.
(4) The inspection of sand, gravel or pebbles shall be based on the same origin, the same specification and the same entry time, and every 100m3 shall be an acceptance batch.
(5) Petroleum asphalt shall be tested in the same place of origin, the same variety and the same label, and every 20t shall be regarded as an acceptance batch, and when it is less than 20t, it shall also be tested as an acceptance batch.
(6) Admixtures must have the manufacturer's quality certificate, which includes the name of the manufacturer, product name, packaging, quality (weight), production date, performance and instructions for use. Before use, the performance test should be carried out according to the number of each incoming equipment.
(7) 200t of fly ash of the same grade is a batch of fly ash from the same factory, and when it is less than 200t, it is also inspected as an acceptance batch. The measurement of fly ash is calculated according to the weight of dry ash (the water content is less than 65438 0%).
(8) Compactness detection of subgrade fill: According to the conditions of this contract section, sand filling method, ring cutter method or nuclear densimeter method shall be adopted. When there is no wheel track on the top surface of the compacted layer, the detection frequency is 8 o'clock when it is 2000m2, and at least 2 o'clock when it is less than 2000m2; At least 4 points should be detected at each abutment back of bridge and culvert structures, and the compactness of each point must meet the specified requirements.
(9) Concrete works shall be vibrated in strict accordance with the specified standards to ensure that the vibrating is compact and free from honeycomb, pits and segregation.
(10) Strengthen the detection of various performance indexes of SBS (modified asphalt mixture) pavement, such as rutting resistance at high temperature, crack resistance at low temperature, fatigue resistance, water stability, pavement durability and smoothness.
4. Factors affecting the quality of common highway materials
In highway construction, quality is the key to engineering construction. Problems in any link or any part will bring serious consequences to the overall quality of the project, directly affect the speed of national construction and the efficiency of highway use, and even cause huge economic losses due to rework and reconstruction. Therefore, the quality of highway engineering and engineering materials are a key factor.
(1) The unplanned supply of materials, irregular stacking, incomplete signboards and mixed stacking, coupled with poor management, make cement, steel and other materials damp, deteriorate and rust, and reduce or lose their original performance; (2) Material inspection is not timely, missed or wrong, and unqualified materials are passed off as qualified materials, resulting in undue quality hazards; (3) Inadequate investigation of soil materials and soil quality of subgrade filling and misjudgment may easily lead to hidden dangers of subgrade quality, such as the treatment of poor geological conditions such as soft soil foundation and collapsible loess, and special supervision should be strengthened in advance; (4) When filling subgrade, the virtual paving thickness must be controlled by layered rolling; (5) The welding, lap joint and weld seam of steel bars are unqualified, which will easily lead to quality accidents if they are not found and controlled in time; (6) Culverts, cover plates, precast beams and other semi-finished components are directly installed on the structure, and the inspection is not timely or the sampling frequency is not enough, which may easily lead to quality accidents.
5. Effective methods to strengthen the quality control of highway construction materials.
(1) The inspection, quality control and quality assurance of raw materials should proceed fundamentally, starting from the constituent materials of the structure. Therefore, it is necessary to choose reasonable and high-quality material sources. The selection of material sources shall be carried out by the person in charge of the site laboratory with the cooperation of the supervision engineer. Investigate gravel (gravel or pebble) yards, cement plants and steel plants along the highway. Check the production license, production qualification and production scale; 2. Check the perfection and advanced degree of factory equipment; Third, check the management system and production capacity; Fourth, check the technical strength and product quality. Then visit the production workshop, randomly take samples, and conduct a performance verification test on raw materials by the contracted artificial laboratory. The other is verified by the central laboratory of the supervision engineer. If the two verification results are qualified, the source of the materials can be considered, and it will be reported to the owner for approval after being approved by the supervision engineer. For the selection of sources of asphalt materials, mineral powder, lime, fly ash, additives, stone and other building materials, as well as the selection of suppliers of finished products and semi-finished products, the supervisor still insists on the source and completion of materials.
Suppliers of goods and semi-finished products should inspect the material manufacturers and processors of finished products and semi-finished products, require all relevant materials that can prove the quality, and go deep into the production workshop to inspect the production equipment, management procedures and production technology. The supervisor should strengthen the on-site supervision of production technology, control the correct process, and conduct random sampling tests on materials. Conduct regular and irregular sampling acceptance tests on products. Check whether the production records are true, focus on key production processes and concealed works, and strengthen supervision and monitoring. Do a good job in quality supervision and management of material sources and finished products before they enter the site.
(2) Strengthen the quality control of local material sources.
The supervisor shall, according to the contractor's mining plan, locate in the material yard, material name, material specification, estimated reserves, planned mining quantity, model and quantity of mining and processing machinery and equipment, processing technology, production flow, technical ability of mining personnel, economic comparison feasibility scheme of self-mining and outsourcing, technical ability of mining personnel, economic comparison feasibility scheme of self-mining and outsourcing, and necessary documents of mining and processing. If blasting requires a permit approved by the local public security bureau, the purchase, storage, storage and use of blasting materials required by the public security bureau should be carefully inspected and implemented. After all preparations are made, the contractor's self-mining plan will be approved and reported to the owner for approval, and the contractor will begin to implement the trial production phase plan in the self-mining plan. At this time, the supervisor will stand by, supervise and manage the contractor's production post in the mining field, and process the trial mining materials into samples for material verification test. Only when the verification results are qualified can the contractor's formal mining plan be approved. Supervision always controls the mining area.
Dynamic production, safe operation and quality assurance provide high-quality materials for high-grade construction. If, during the monitoring process, the supervisor finds that the materials are deteriorated and fail to meet the specification requirements after sampling verification, the supervisor shall immediately order the mining to stop, and the mined materials are prohibited from being used in the project. Absolutely put an end to unqualified products entering the construction site.
(3) Ensure the quality and protection of the site yard.
After all kinds of materials enter the site, the supervisor shall supervise the contractor, yard personnel and laboratory personnel to accept, store, stack, keep and protect the materials, and notify the supplier (goods) to enter the construction yard with the materials (finished products) with the material (finished products) certificate and factory inspection report. Three days before the materials enter the site, the supervisor shall conduct a comprehensive inspection of the contractor's on-site material warehouse (yard). Check whether the cement warehouse, steel warehouse, asphalt shed and mineral powder shed are equipped with moisture-proof deterioration facilities according to the material performance, whether the yard has hardened, whether the surrounding area can be drained, whether the yard and material warehouse (shed) have perfect management rules, systems and management responsibilities, and set up identification cards for each yard, pile and material warehouse (shed). The materials are stacked neatly and geometrically, and can be used at any time after passing the test.
(4) Inspection shall be conducted according to regulations, and sampling shall be conducted according to frequency.
During the construction process, the supervisor supervises the on-site laboratory to conduct full-frequency self-inspection tests on all kinds of incoming materials, and on this basis, the owner rechecks the materials at a frequency greater than 5%. If the contractor's self-inspection test is qualified, but the supervision sampling is unqualified, it will be ordered to make rectification. If the sampling frequency is still unqualified after increasing, the supervisor will order the unqualified materials to be removed from the site for serious treatment. At the same time, before stacking new materials, clean up the material warehouse (shed, yard). Material quality control is the premise of engineering quality control. Only by strictly controlling the self-inspection of enterprises, social supervision and government supervision can the project become a high-quality project, a high-quality project and a model project.
The detailed information of "Testing and Quality Control of Common Highway Materials" can be found in Zhong Da Consulting & Construction Link, and all relevant construction information you want is available.
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