Cast in place structures (formwork)
construction of lightweight aggregate concrete
1 scope
This technology is applicable to on-site
mixing of ceramic, light pumice aggregate, sand the whole cast of lightweight
aggregate concrete formwork.
2 construction preparation
2.1 materials and equipment:
2.1.1 lightweight aggregate:
Pumice: maximum size should not be larger
than 20mm, do not allow more than the maximum size of twice times more
particles. Grading requirements for 5mm mesh not greater than 90%, through the
10MM mesh 30%~70%; 200mm mesh not greater than 10%. Void fraction is less than
50%, 1h water absorption ratio is not greater than 25%, clay is less than 2%,
loose bulk density, cylinder compressive strength in accordance with the design
requirements.
Ceramic: the requirements are the same as
above, and shall not be mixed or inclusions of clay blocks.
2.1.2 sand: sand or coarse sand sediment
when the concrete strength grade of C10~C30, and no greater than 5%, when
concrete strength is greater than, the C30 is not greater than 3%.
2.1.3 cement: No. 325, No. 425 Portland
slag cement or Portland cement.
2.1.4 additive: product quality certification,
dosage must be determined through laboratory and technical performance in line
with the relevant provisions of the standards.
2.1.5 major equipment: mixer, skip, carts,
scales, inserted vibrator, shovel, tiepan, wood float, small shovels, small spoons,
buckets, rubber pipes, additive metering containers.
2.2 operating conditions:
2.2.l raw materials including cement,
lightweight aggregates, admixtures comes into play, such as checking the
factory certificate, its technical performance indicators must comply with the
requirements, and retesting should be lightweight, 2003 (less than 200m3), must
be tested: loose bulk density, particle size distribution, cylinder compressive
strength, 1h water absorption. Natural light weight aggregate testing sediment,
reinspection is not qualified, the reasons should be identified and measures
taken.
2.2.2 laboratory test to determine the
distribution ratio and the slump. The strength of lightweight aggregate
concrete density shall meet the design requirements.
2.2.3 light aggregate pile site drainage
measures, try to keep particles when using mixed evenly, avoid small particles
separated by natural graded when stacked, its height should not be more than
2m, to prevent leaves, mixed with earth or other harmful substances.
2.2.4 template seam should be tight if when
using shoe trees, watering must be moist. Formwork for exterior wall outer
swallow ring beam spot measures should be taken to prevent leakage.
2.2.5 familiar with the drawings of the
design before construction requirements, technical clarification.
3 operational processes
3.1 process
Job preparation materials measurement → → → mixing → transport →
construction → vibration maintenance
3.2 material measurement: aggregate, and
cement, and water and plus agent are by weight meter, aggregate measurement
allows deviation should is less than ± 3%, cement, and water and plus agent
measurement allows deviation should is less than ± 2%, light aggregate should
be in mixing Qian pre wet, so according to tie than determine water Shi, also
must calculation aggregate of moisture (mixing Qian should determination
aggregate containing water rate), do corresponding of adjustment, in mixing
process in the should often began assessing, rainy day or slump exception
should timely determination containing water rate, adjustment water. W/c total
available water/cement ratio, the total water consumption should include a mix
of effective water demand and water absorption of light weight aggregate LH in
two parts.
3.3 mixing:
3.3.1 charging sequence: using down mixer
with 1/2 water. Then add the coarse and fine aggregates and cement mixing 1min,
then add the remaining water and continue stirring at least 2min. Compulsory
mixer, first add fine cement and aggregate, coarse aggregate, mixing 1min add
water stir not less than 2min.
3.3.2 the mixing time should be slightly
longer than the ordinary concrete, the mixing time is about 3min. In the mixing
process of lightweight aggregate concrete and lightweight aggregate absorb
water, it should be treated with the slump in the construction of concrete
values to control water consumption, and control the water/cement ratio, so
that more relevant year is easy to master.
3.4 transport: lightweight water-absorbing
ability at an early stage is very strong, so should be as short as possible in
the construction of concrete mixers were exported to job placement, this
process of time, generally not more than 45min. Wish to skip directly to the
mixer outlet hanging to job placement, to avoid or reduce the Middle out of
luck, if it leads to mixture of poor and vulnerable, the slump goes, suitable
artificial two-stage mixing before pouring.
3.5 pouring: should continuous
construction, not left or less left construction sewing, pouring concrete
should layered for, on big template engineering, each layer pouring height
first layer not should over 50cm, yihou each not over LM, if left construction
sewing should vertical left in both inside and outside wall handover at and the
water paragraph boundaries at, set wire network or blocking head template,
continues to construction Qian, must will joint at cleanup clean, watering wet,
then again pouring concrete.
3.6 vibration: light weight aggregate
density light, easily causing the mortar to sink, lightweight aggregate float.
Quick vibrating needle insert slow pulling, vibration points to appropriate
encryption, distribution, its vibrating spacing spacing is less than normal
concrete, should not be greater than 1 time times the radius of the vibration,
insertion depth should not exceed the construction height. Time should not be
too long, preventing layered segregation. Tools for concrete surfaces will be
exposed in lightweight aggregate in mortar, and then use wood trowel the
surface smooth.
3.7 conservation: the stripping strength of
lightweight aggregate concrete under normal temperature should be greater than
1MPa. Water conservation or covered film in time after stripping moisture
conservation, prevent shrinkage cracks in the water. Complete casting formwork
when the exterior wall shelf bracket, wall strength control of concrete not
less than 7.5MPa, safety requirements for ensuring shelf bracket.
3.8 in winter: winter programme
implementation.
3.8.1 shall not use aggregates with ice and
freezing.
3.8.2 transport container for concrete
insulation measures.
3.8.3 winter period light aggregate
impossible watering pre wet, dang using natural dried state of light aggregate
Shi, should adjustment slump control value, General take 12~14cm, than at room
temperature Xia increases 4~6cm, concrete out tank Hou by transport to pouring
locations about fell to 8~10cm, can guarantee get can vibration pound dense of
concrete, and can control concrete not due to plastic had big, occurred rough
aggregate floating, and caused segregation phenomenon.
3.8.4 mixing pumice concrete can be used on
the secondary material, method of two-stage mixing. First floating on stones,
admixtures (fly ash) mixing of water and 1/3 1min, the second is expected to be
on cement, sand, additives and stir the rest of the water to join to improve
the workability of the concrete, and avoid holes absorb pumice admixtures.
3.8.5 template removed and the walls hung
when the tripod, the strength of concrete conditions block needs to be done.
Intensity control 4MPa and 7.5MPa, respectively. Ensure mixing of antifreeze
concrete the frozen critical strength and hang tripod safe.
4 quality criteria
4.1 project:
4.1.1 use of lightweight aggregate concrete
cement, aggregates, admixtures, mixing ratio, measuring, mixing, conservation
and treatment of construction joints, must conform to the specifications and
requirements of the relevant standards, check the factory certificate, the test
report.
4.2.2 strength of lightweight aggregate
concrete in accordance with design and evaluation standard of inspection
requirements, and density meet the design requirements.
4.2 Basic project:
Vibrating compaction, surface, honeycomb,
Matt surface, does not reveal tendons, joints and no holes slag layer.
4.3 allowable deviation, as shown in table
4-33.
Table 4-33
Tolerance (mm)
Multi-layer high
1 axis displacement 8 5 foot check
Storey ± 10 ± 10
Full height ± 30 ± 30
3 section dimensions +5-2 + 5-2 ' check
Check every 5, 5 2m supporting plate
Overall height of 1 ‰ and ≤ 20 1 ‰ and ≤ 30 using a
theodolite or hanging and foot check
5 smooth 4 4 2m m on foot and wedged feeler
Gage check
Center line of embedded steel plate of 6
and 10 10
7 embedded pipe, reserved holes, embedded
bolt centerline offset 5 5
8 is hole centerline offset 15 15
5 finished product protection
5.1 when pouring and vibration protection
of good holes, embedded and embedded pipes, boxes of water, electricity and so
on.
5.2 enter lightweight aggregate to take
good care of to prevent crushing and mixed with debris.
5.3 concrete pouring and tamping and
finished to keep the exposed reinforcement position correctly.
6 quality problems to be noticed
6.1 concrete slump and instability: water
master no, changes in the moisture content of lightweight aggregate,
determination of adjustments in a timely manner at the end of water.
6.2 poor and vulnerable: insufficient
mixing time, the material too quickly.
6.3 surface light aggregate exposure:
concrete vibrating when the accept header, seeking and vibration on the
surface, has yet to carry out pressure and smooth.
6.4 low strength: measurement is not
accurate, vibration is not dense, poor conservation.
6.5 Cha imperfect: the outer wall beam Cha
shall be no leakage, pay attention to the vibration density.
7 quality records
This standard shall meet the following
quality records:
7.1 materials (cement, sand, lightweight
aggregates, admixtures, etc)-factory certificates, test reports.
7.2 test report, strength evaluation for
lightweight aggregate concrete block.
7.3 concrete construction records.
7.4 project for quality inspection and
assessment.
7.5 hidden inspection, inspection records.
Winter construction of 7.6 recorded.
7.7 design changes, record of negotiation.
7.8 other technical documents.
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