Concrete mixing
1 scope
This technology is applicable for
industrial and civil buildings of the concrete mix.
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 report.
2.1.2 sand: sand particle size and origin
should meet the requirements of concrete mix order. Sand clay content: when the
concrete strength ≥ C30, clay content ≤ 3%; when the concrete strength grade <C30, clay 5%, frost
resistance, impermeability requirements, the sediment shall be ≤ 3%. Content
of mud in sand (greater than 5mm of pure clay), when the concrete strength ≥ C30, its
content should be ≤ l%; when the concrete strength grade <C30, its content should be
less than 2%, frost resistance, impermeability requirements, its content should
be less than l%. Sand should have the test report form.
2.1.3 the gravel (gravel or pebbles): stone
size, grade and origin should meet the requirements of concrete mix order.
Stones of needle and plate-shaped particles
content: when the concrete strength ≥ C30, ≤ 15%, when
C25~C15 is strength of concrete should be ≤ 25%.
Stones of clay (less than 0.8mm of total
dust, silt and clay content): when the concrete strength ≥ C30, ≤ 1%, when
C25~C15 is strength of concrete should be ≤ 2% when on the
frost resistance of concrete requirements should be ≤ 1%.
Stones with mud content (greater than 5mm
of pure clay): when the concrete strength ≥ C30 should be ≤ 0 5%; when
the concrete strength grade <C30, should be ≤ 0.7%; when the concrete
strength grade ≤ C10, should be less than l%.
Stone should have a sample report.
2.1.4 water: potable water should be used.
Other water, the water quality must meet the standards for concrete mixing
water (JGJ63 189) requirements.
2.1.5 admixtures: concrete admixtures, used
by manufacturers and brands, the mix order requirements. Admixtures shall have
certificates of quality and use, and should have entry 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, there are mixed with other materials, such as zeolite and UEA
expansion agent): varieties of mixed materials, used by manufacturers and
brands, the mix order requirements. Hybrid materials have certificates of
quality and use, and should approach the test report. Mixed material must also
have a volume test.
2.1.7 main machinery: concrete mixers
should be compulsory mixer takes precedence, to using down mixer. 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 there are two-wheeled carts,
forklift, loader, sand transport Hopper, as well as supporting other devices.
Field test instruments, such as slump test equipment, test mode.
2.2 operating conditions:
2.2.1 laboratory issued concrete orders,
and convert each actual mix used, and published in place of mixing ingredients
on the plate.
2.2.2 all raw materials inspections, all
should conform to the mix order request.
2.2.3 mixers and their ancillary equipment
shall be operational flexibility, safety and reliability. 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 part has been hidden to be pouring
concrete inspection, preflight procedures, concrete request has been approved
by the relevant managers.
2.2.7 released concrete mix, identification
should be opened. Opening stock of the work carried out and meets the
requirements.
3 operational processes
3.1 basic flow:
3.2 each Taiwan class began Qian, on mixer
and the Shang material equipment for check and commissioning; on by with
measurement apparatus for check and set pounds; proofing construction tie than;
on by with raw materials of specifications, and varieties, and origin, and
grades and the quality for check, and and construction tie than for check; on
sand, and stone of containing water rate for check, as has changes, timely
notification test personnel adjustment water. After all checks meet the
requirements before they can open mixing concrete.
3.3 measure:
3.3.1 sand, stone measures: when feeding on
a wheelbarrow, must weigh, discharge up less. Hopper and ancillary measuring
equipment, with automatic or semi automatic material, need to adjust the amount
of aggressive closes early, in order to ensure accurate measurement. Sand and
stone measuring deviation should be allowed to ≤ ± 3%.
3.3.2 cement-weighting: mixing using bagged
cement, for each entry, the cement should check 10 bags of weight and measure
the average weight of each bag. Calibration weight is less than to open the bag
up, or subject to the actual cement weight of each bag, adjusting the amount of
sand, stone, water and other materials, according to each concrete mix * set of
construction mixture ratio. When mixing cement in bulk, should be conducted at
precise measurement. Cement-weighting the deviation should be allowed to ≤ ± 2%.
3.3.3 measurement of admixtures and
mixtures: powdered admixtures and mixtures should be according to the
construction mixture ratio per plate materials, admixtures and mixtures placed
in advance are measured in the warehouse, and small package shipping to stir
and set aside. Liquid admixtures to ad-mix, with a hydrometer to check the
concentration, the amount of barrel measurement. Measurement tolerances of
admixtures and mixtures shall be ≤
± 2%.
3.3.4 metering of water: the water must be
measured, the deviation should be allowed to ≤ ± 2%.
3.4 preparation: mixing concrete on site,
good is generally measured on the collection of the raw material in the hopper,
hopper into the mixing drum on. After measurement, the water and liquid
admixtures, feeding into the mixing Drum at the same time, directly into the
mixing tube. Raw material collection into the sequence is as follows:
3.4.1 when no admixtures, mix, and entered
the order of the hopper for gravel, cement and sand.
3.4.2 when mixed-doped material, its order
is gravel, sand, cement, mixture.
3.4.3 when mixing dry powder additive, the
order for these stones, admixtures, cement, sand into order as gravel, cement,
sand and admixtures.
3.5 the first concrete mixing system
operation:
Concrete mix first set to work at a time,
mixing drum of idling for a few minutes before adding water, mixing tube is
fully moist, the remaining water evacuation.
When stirring first set, losses due to the
viscosity of mortar wall, therefore, dosage should be according to the mixing
ratio of stones in half.
Starting from the second set, at a given
mix feed.
3.6 time control: the shortest time
according to table concrete mixing 4-28 control.
Concrete mixing time (s) in table 4-28
Mixer discharge capacity (l)
<250 250~500 >500
Forced 60 90 120
Since falling 90 120 150
Forced 60 60 90
Since falling 90 90 120
Note: l. Concrete mixing means the shortest
time since all the material into the mixing drum, to start unloading time;
2. when additives are mixed with, mixing
time should be extended appropriately;
3. winter construction of mixing time
should be taken when mixing time of 1.5 times at room temperature.
3.7 out of material: the material at, a
little discharge, visual appearance quality of the mix, such as Visual
inspection before they can discharge. Each concrete mix must be made.
3.8 concrete mixing quality checks:
3.8.1 check mixing concrete the varieties,
specifications and quantity of raw materials used, every work shift at least
twice.
3.8.2 checking concrete slump and
workability, every work shift at least twice. Concrete mix should be and mix,
same color, good flowability, cohesion and retention, no bleeding, not
segregation. Does not meet the requirements, should find out the reasons to
adjust.
3.8.3 in each class of work, when changes
are due to outside influence of mix proportion of concrete (such as rain or raw
material changes), you should check in time.
3.8.4 concrete mixing time should be
checked at any time.
3.8.5 indwelling blocks as follows:
3.8.5.1 each mix 100 and no more than 100m3
with Proportioning of concrete samples shall not be less than one.
3.8.5.2 each work class mixing proportion
of concrete is less than 100 sets, the sample shall not be less than one.
3.8.5.3 concrete structure, each cast
floors with concrete mix, the sample shall not be less than one.
3.8.5.4 impermeable concrete requirements,
should be required to retain impermeability test block.
Should be retained for at least one set of
standard specimen per sample, sample cured in same condition retained the
number of groups. According to technical requirements. In order to ensure
retention of specimens representative, should end after the third set to
stirring 30min before sampling.
Winter construction of concrete mixing 3.9:
3.9.1 continuous stable 5d outdoor
temperature below 5 ℃, mixing concrete winter construction measures should be taken, and
the sudden drop in the temperature of the freezing measures should be timely.
3.9.2 preparation of winter construction of
concrete, should be preferred Portland cement and ordinary Portland cement,
cement grade should not fall below No. 425, minimum cement dosage should not be
less than 300kg/M3, water/cement ratio should not be greater than 0.6.
3.9.3 winter use chlorine-free antifreeze
salts, freeze against demanding concrete. Appropriate use of air-entraining
agent or air-entraining water-reducing agent. If the antifreeze is mixed with
chlorine salts, should strictly control the volume, and strictly enforce the
provisions relating to antifreeze is mixed with chlorine salts.
3.9.4 aggregates for concrete must be clean
and shall not contain ice, snow, ice and frost cracking of minerals.
3.9.5 winter should give priority to the
use of hot water method for mixing concrete. Water and heating temperature
should be determined according to the thermal calculation of aggregate, but
shall not exceed the provisions of table 4-29.
Maximum temperature of mixing water and
aggregate table 4-29
Aggregate project mixing water
Labels smaller than No. 525 ordinary
Portland cement and slag Portland cement 80 60 ℃
Label larger than No. 525 ordinary Portland
cement and slag Portland cement, 60 ℃ 40 ℃
Cement directly heated before use and
should be transported inside a greenhouse store.
When the aggregate is not heated, water can
be heated to 100 degrees, but the cement should not direct contact with more
than 80 ¡æ water. Feed first input aggregate and heat the water, and then put
into cement.
3.9.6 before concrete mix, hot water or
steam cleaning the Blender, mixing time should take the temperature of 1. 5
times. Concrete mixing machine temperature should not be below 10 ℃, casting
temperature shall not be less than 5.
3.9.7 winter concrete mixing quality checks
in addition to complying with the provisions of article 3.8, but should carry
out the following checks:
3.9.7.1 check the admixture dosage.
3.9.7.2 measurement of water and additive
solution the temperature of the heating temperature and adding mixers and
aggregate.
When discharged in 3.9.7.3 measurement of
concrete mixer temperature and pouring temperature.
More than check each class should at least
be measurement checks four times.
3.9.7.4 retaining concrete block addition
should meet the 3.8. the provisions of article 5, should be not less than two
additional groups and structure of sample cured in same condition, respectively,
for inspection before freezing of concrete strength and maintenance 28D of
concrete strength at room temperature.
4 quality criteria
4.1 project:
4.1.1 cement used in concrete, aggregates,
admixtures, mix size, variety and quality in compliance with the relevant
provisions of the standards.
Inspection methods: inspection raw material
factory certification, test report.
4.1.2 concrete strength evaluation should
meet the requirements.
Methods: checking reports of pressure test
for strength and strength estimation of concrete block material.
4.2 Basic project:
4.2.1 should be and mix of concrete, the
same color, has a good workability.
Inspection method: Visual check.
4.2.2 fresh concrete slump should meet the
requirements.
Methods: field measurement and check
records.
4.2.3 when winter construction, water,
aggregate heating temperature and temperature shall conform to the requirements
of concrete mixing machine.
Methods: field measurement and check
records.
5 quality problems to be noticed
5.1 uneven strength or strength of concrete
strength deviation, is frequent quality problems is the quality problem of
structural safety. Preventing quality issues need to be integrated, in addition
to concrete delivery, placement, maintenance and other things need to be
strictly controlled in concrete mixing stage with special attention. To control
the quality of raw materials. We should earnestly implement the mixture ratio,
strict ingredient metering of raw materials.
5.2 quality problems of concrete cracks
often occur. Due to many reasons. In the mixing stages, if mud content of sand,
stone, large amount of water, the use of obsolete and excessive amount of
cement or cement and, may result in shrinkage cracks. In the mixing stages, is
to strictly control the quality of raw materials, seriously implement the mix,
strict measures.
5.3 concrete mix of poor and vulnerable,
slump does not meet the requirements. Cause this type of quality problem is in
many ways. Water cement ratio most of them; the second is the stone of poor
grade, pins, plate-shaped particles with too much; the third is mixing time is
too short or too long. Solutions from the above three aspects.
5.4 winter construction of concrete is
prone to frost damage. Solution is to seriously implement relevant provisions
in the winter, in the mixing phase of the heating of aggregates and water
temperature, ensure coagulation for the machine temperature.
Note 5.5 admixtures for cement, admixtures,
stored for safe keeping. Cement cement, rain and damp; cement factory for more
than three months should be the test. Admixtures and mixtures in order to
prevent damp and bad, to specifications, respectively, in order to prevent
misuse.
6 quality records
This standard shall meet the following
quality records:
6.1 cement factory prove quality.
6.2 cement into the test report.
6.3 quality additives proven.
6.4 additives enter the amount of test
reports and test reports.
6.5 quality mixtures proved.
6.6 test mixture into the test report and
the content of the report.
6.7 test report of sand.
6.8 stone test report.
6.9 notice of concrete mix.
6.10 strength concrete block pressure test
report.
6.11 strength evaluation of concrete
records.
6.12 concrete logs (including Shi Rizhi in
winter).
6.13 concrete open identification.
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