Mixing technology of lightweight aggregate concrete

Mixing of lightweight aggregate concrete

1 scope

Technology standards for the construction of lightweight aggregate concrete mix preparation, processes, quality standards and quality inspection, and more.

This technology is applicable for industrial and civil buildings of lightweight aggregate concrete mixing on site.

2 construction preparation

2.1 materials and equipment:

2.1.1 cement: cement, label, factory and trademark should comply with the notice requirements of concrete mixing ratio. Cement factory certification and entry test.

2.1.2 sand: sand particle size and origin should meet the requirements of concrete mix order. Clay in the sand; when the concrete strength class ≥ C30, the sediment should be ≤ 3%; when the concrete strength grade <C30, the clay should be ≤ 5%. Content of mud in sand (greater than 5mm of pure clay): when the concrete strength ≥ C30, should < 1%; when the concrete strength grade <C30, ≤ 2%. Sand should have the test report form.

2.1.3 light-weight aggregate: light weight aggregate (ceramsite or pumice, etc), size, origin should comply with the notice requirements of concrete mixing ratio. Light-weight aggregates should have quality certificates and entry test reports. Must test items are: aggregate sieve analysis test aggregate density; cylinder compressive strength of coarse aggregate; water absorption of coarse aggregate test.

Light coarse aggregate gradation shall meet the requirements in table 4-30, the natural distribution of void fraction should not be greater than 50%. The maximum particle size should not be larger than 20mm. Its clay content is less than 2%.

Light coarse aggregate gradation table 4-30

Opening size DMin (5) 1/2dmax (10), DMax (20) 2dmax (2x20)

Sphere and single sieve residue accumulated over 90 no regulation of size ≤ 10 0

Ordinary mixed grade ≥ 90 30~70 by weight ≤ 10 0

Mix gradation of gravel-type (%) ≥ 90 40~60 ≤ 10 0

Light fineness modulus of sand should not be greater than 4.0, which today than 5mm should not be greater than 10% of sieve remainder (by weight).

The density of light-weight aggregate, lightweight coarse aggregate strength of cylinder compressive strength and should comply with the design requirements.

Light and natural water absorption of light weight coarse aggregate rate provisions other rate of water absorption of light weight coarse aggregate 1h is less than 22%.

2.1.4 water: potable water should be used. Other water quality must meet the standards for concrete mixing water (JGJ63 189) requirements.

2.1.5 admixtures; lightweight aggregate concrete admixtures, used by manufacturers and brands, the mix order requirements. Admixtures shall have certificates of quality and use, and should be in for a test report on indicators. State regulations require certification of products, should also be permitted documents. Additives must have volume test.

2.1.6 mixed materials (primarily fly ash at present): varieties of mixed materials, used by manufacturers and brands, the compound form of requirements. Hybrid materials have certificates of quality and use, and should approach the test report. Mixed material must have a volume of tests.

2.1.7 main equipment: sand lightweight concrete should be compulsory mixer takes precedence, since fall mixer. Light concrete forced mixer should be used. Metering equipment commonly used scales or electronic measuring equipment. Measuring meter, time relay can be used to control the water flow meter tube or tank water level marks the meter. Feeding equipment such as two-wheeled carts, forklifts, loaders and of coarse and fine aggregate hopper and supporting other devices. Field test instruments, such as slump test equipment, test mode.

2.2 operating conditions:

2.2.1 laboratory has issued notice of lightweight aggregate concrete mix, and convert each actual mix used, and published in place of mixing ingredients on the plate.

2.2.2 use of raw materials have been examined, all should conform to the mix order request.

2.2.3 mixer and its supporting equipment is flexible, secure, and reliable. Power supply and distribution system in accordance with requirements, safe and reliable.

2.2.4 all verification of measuring instruments must have valid identification. Clean platform below and the surrounding sand, stone, measuring instruments sensitive and reliable, and press set mix special points.

2.2.5 administration personnel to the job the team mix, operating procedures and safety technology gives the low-down.

2.2.6 need lightweight aggregate concrete pouring works site has been hidden inspection, preflight procedures, lightweight aggregate concrete request has been approved by the relevant managers.

2.2.7 new release of lightweight aggregate concrete mix, identification should be opened. Opening stock of the work carried out and meets the requirements.

3 operational processes

3.1 basic flow:

Lightweight aggregate concrete production process flow chart

3.2 the stacking and storage of raw materials:

3.2.1 light coarse aggregate size-stacking, and waterproof and drainage measures in order to prevent moisture changes. Mixed size-when stacking, stacking height should not be more than 2m to prevent particle size segregation, gradation balance. When used with normal aggregate, should make weight aggregate storage respectively, non-hybrid, to ensure accurate ingredients.

3.2.2 cement, admixtures and additives should be protected against rain, moisture-storage warehouse, to prevent cement induration, changes of moisture content of admixtures, powdered additive failure, liquid additive concentration.

3.3 sampling measurement and metering of raw materials:

3.3.1 measurement of light-weight aggregate: suitable for volume measurement, weight measurement can be adopted, but we must strictly testing moisture content of aggregate, removing moisture content of its provisions other than the weight of water in order to ensure accurate ingredients. Ordinary sand weight measurement. Volume metering, you must use a special measuring cart or special volume meter, each disk must be strictly measured.

Weight measurement, use a cart must be weighed, unloaded up less. Hopper and ancillary measuring equipment, with automatic or semi automatic material, need to adjust the amount of aggressive door switch in advance, in order to ensure accurate measurement.

Measurement of light-weight aggregate allowable deviation of ≤ ± 3%.

3.3.2 cement measure: when using bagged cement, have to press the incoming batch of random measurement. Weight per batch entry should check 10 bags of cement, and calculates the average of the actual weight of each bag. Calibration weight is less than up to open the package, or subject to the actual weight per bag of cement, adjust the coarse and fine aggregates, amount of water and other materials, according to the given proportion to redefine each mix. When bulk cement is used, each accurate weighing. Cement-weighting the deviation should be allowed to ≤ ± 2%.

3.3.3 measurement of admixtures and mixtures: with bags of powdered admixtures and mixtures should be entry check 10 bags per batch weight, and measure the average weight of each bag, is smaller than the calibration weight to be replenished. For bulk or packaged admixtures, construction mixture ratio measuring the amount of each advance in its repository, and in the form of small packages shipped to stir and set aside. Liquid admixtures to ad-mix, with a hydrometer to check the concentration, graduated cylinder measure. Admixtures and mixtures of ≤ ± measurement deviation should be allowed to 2%.

3.3.4 mixing water must flow meters measure reading measurement, pipe or water tank water level mark the meter. Every measure allowed deviation of ≤ ± 2%.

3.4 the feeding process of lightweight aggregate concrete mixing procedure:

3.4.1 lightweight aggregate concrete mixing of the water absorption rate of less than 10%, and secondary material processing procedures should be used. Aggregate contract 1min 1/2 water into blender and mix, then add cement composite seconds, then add the remaining water and admixtures, continue stirring until 2min, feeding and mixing procedure for this method is:

1/2 total water consumption

Coarse aggregate 1/2 total water consumption of cement, admixtures

Stir mixture with water and aggregate concrete mix

Fine aggregate

Lightweight aggregate concrete mixing water absorption greater than 10%, should adopt the wet aggregate feed and mixing processes. Light coarse aggregate prior to mixing the wet, coarse aggregate, cement, fine aggregate into Blender in the order summary, mixing Drum mixing 0.5min into Blender together again, and then with water and additive mixing 2.5min, feeding and mixing procedure for this method is:

NET consumption of water → coarse aggregate admixtures

Cement mix concrete mix

Fine aggregate

3.4.3 using down mixer feeding and mixing processes of the program are: to join the 1/2 per cent of the total volume of water, then add the coarse and fine aggregates and cement mixing Lmin, then add remaining water, stir 2min, feeding and mixing procedure for this method is:

Coarse aggregate 1/2 total water consumption water consumption 1/2

Mixture of cement mix concrete mix

Fine aggregate

3.4.4 using forced mixer feeding and mixing processes are: investment and coarse aggregate, cement, fine aggregate, Lmin stir, then add water to continue mixing at least 2min. Feeding and mixing procedures for this method is:

Total water consumption of coarse aggregate admixtures

Stir the mixture of cement mix concrete mix

Fine aggregate

3.5 first mixing concrete problems of:

3.5.l before mixing concrete, add water to idle for a few minutes, be fully after wet mixing drum, water drain.

3.5.2 when first mixing concrete, cement mortar mix damage caused sticky wall. Be taken pre-mixing method, that is given with a design of lightweight aggregate concrete mix proportion of raw materials into the mixer, which should be extended more than 1 time, to be part of the mortar paste on the wall in a blender, then rest of mixture unloading (secondary feed mix used), then you can mix properly.

3.6 time control and inspection: lightweight aggregate concrete mixer-the minimum amount of time than the conventional concrete mixing time should be extended 60~90s, generally 180s; when mixed with additives, and mixing time should be extended appropriately.

3.7 out of material: material should be a little discharge, visual appearance quality of the mix, such as Visual inspection before they can discharge. Each mix must be made.

3.8 lightweight aggregate concrete mixing quality checks:

3.8.1 check the mixing of raw materials used in lightweight aggregate concrete varieties, specifications and content of every work shift at least twice. Rain during construction on the moisture content of lightweight aggregate to increase inspection and determination of the number.

3.8.2 check light aggregate concrete slump and workability in pouring stations, each class more than twice. Rain periods, and changed the level of lightweight concrete winter construction, to strengthen the detection times.

3.8.3 in each class of work, when lightweight aggregate concrete due to outside influences have changed, should be checked in a timely manner.

3.8.4 lightweight aggregate concrete mixing time should be checked at any time.

3.8.5 check the appearance quality of light weight aggregate concrete mix should be, mixing, color consistency, good flowability, cohesion and retention, no bleeding, not isolation. Does not meet the requirement, the reasons should be checked, adjusted in a timely manner.

3.8.6 indwelling blocks as follows:

Mixing 3.8.6.1 each 100 and not more than 100m3 of mix proportion of concrete, the sample shall not be less than one.

3.8.6.2 each class mixing proportion of concrete is less than 100 sets, the sample shall not be less than one.

3.8.6.3 for in-situ concrete structure, each cast floors with concrete mix, the sample shall not be less than one.

3.8.6.4 should be retained for at least one set of standard specimen per sample, sample cured in same condition retained group, according to technical requirements.

Ensure indwelling blocks representative should be before the end of the third set after mixing concrete to mix between the 30min sample.

3.9 winter construction of lightweight aggregate concrete mixing: Meanwhile, demand for raw materials, mixing time, raw material heating, mixing tank temperature requirements, should earnestly implement the standard 3.9 in concrete mixing process and the code for construction and acceptance of concrete structures.

3.9.1 aggregate shall not contain snow and a frozen ball.

3.9.2 mixing of lightweight aggregate concrete in winter should be used on the secondary, secondary mixing processes (see section 3.4.l of the mixing process) in order to improve the workability of light aggregate concrete.

3.9.3 should be noticed in winter testing moisture content of aggregate, timely adjustment of water, given the slump in time to different control value. Slump increased 4~6cm should generally be higher than room temperature, to ensure its good flowability, cohesion and retention.

4 quality criteria

4.1 project:

4.1.1 lightweight aggregate concrete used in cement, aggregates, admixtures, specifications of mixture, variety and quality must meet the construction standards and regulations.

Inspection methods: inspection raw material factory certification, test report.

4.2.2 assessment of strength of lightweight aggregate concrete block, you must press the standard of inspection and evaluation of concrete strength (GBJ107 187) of the sampling system.

Check: check strength of lightweight aggregate concrete block pressure test reports and strength evaluation of materials.

4.2 Basic project:

4.2.1 should be and mix of light aggregate concrete, the same color, has a good workability.

Check method Visual check.

4.2.2 slump of lightweight aggregate concrete mixes should conform to specifications or mix order requirements.

Methods: field measurement and check records.

4.2.3 winter water, aggregate heating temperature and concrete mix temperature should meet the requirements of construction specifications.

Methods: field measurement and check records.

5 quality problems to be noticed

5.1 mix incomplete mixing. Different colors: the main reason is the lack of time.

Winter construction and in particular by ensuring the additive, and sufficient time to mixture stirring.

5.2 poor and vulnerable: its mix of loose non-stick together, rising segregation of aggregates, or mix to form a mission should not be poured. Main reasons are: Lightweight Aggregate Gradation worse; sand percentage too small; raw material metering inaccuracy; or short mixing time. Should be carefully overcome these deficiencies, in order to ensure good workability of the mix.

5.3 mixing the slump is not stable. Mainly due to water have not been accurate, coarse and fine aggregates failing determination of moisture in failing to adjust the water. Followed by water measurement is not accurate, water consumption fluctuating. This phenomenon must be overcome to ensure the quality of mixture.

5.4 when you use the additive should be in aggregate after absorbing water, add. In order to avoid excessive absorption of aggregate porosity on admixture. Particularly liquid admixtures, used when unexpected wet aggregate, additives and residual water should be added. Liquid made from powdered admixtures according to law before joining or cement mixtures added to ensure mixing.

6 quality records

This standard shall meet the following quality records:

6.1 cement factory-certified certificate or test.

6.2 cement the second interview.

6.3 test report of sand.

6.4 lightweight fine aggregate test report form.

6.5 light coarse aggregate test report form.

6.6 admixture product certification and quality certificates.

6.7 additives enter the amount of test reports and test reports.

6.8 fly ash factory certificate.

6.9 fly ash tests report.

6.10 concrete mix order.

6.11 concrete logs (including Shi Rizhi in winter).

6.12 concrete open identification.

6.13 strength concrete block pressure test report.

6.14 concrete strength evaluation records.

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