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GB 50496-2018: PDF in English GB/T 50496-2018
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
UDC
P GB/T 50496-2018
Standard for construction of mass concrete
ISSUED ON. APRIL 25, 2018
IMPLEMENTED ON. DECEMBER 01, 2018
Issued by. Ministry of Housing and Urban-Rural Development of PRC.
State Administration for Market Regulation.
Table of Contents
Foreword... 5
1 General provisions... 8
2 Terms and symbol... 8
2.1 Terms... 8
2.2 Symbol... 10
3 Basic requirements... 13
4 Materials, mix proportioning, production and transportation... 14
4.1 General requirements... 15
4.2 Materials... 15
4.3 Design of mix proportioning... 16
4.4 Production and transportation... 17
5 Construction... 18
5.1 General requirements... 18
5.2 Technology preparation... 19
5.3 Formwork... 20
5.4 Placing... 20
5.5 Curing... 21
5.6 Construction in special climate... 22
5.7 Sampling in site... 23
6 Temperature monitor and control... 23
Appendix A Computing method for concrete pump output and carriers... 26
Appendix B Computing method of thermal stress and shrinkage stress during
construction of mass concrete... 27
Appendix C Computing method of insulation layer thickness of mass concrete... 37
Explanation of wording in this standard... 40
List of quoted standards... 41
Standard for construction of mass concrete
1 General provisions
1.0.1 This standard is formulated in order to implement national technical and economic
policies in mass concrete construction, ensure project quality, achieve advanced
technology, reasonable process, resource saving, environment protection.
1.0.2 This standard applies to mass concrete construction in concrete structures. It is
not applicable to the construction of roller compacted concrete and hydraulic mass
concrete.
1.0.3 In addition to complying with this standard, mass concrete construction shall also
comply with the relevant current national standards.
2 Terms and symbol
2.1 Terms
2.1.1 Mass concrete
A large volume concrete which has a minimum physical dimension of not less than 1
m, OR concrete which is expected to cause harmful cracks due to temperature changes
and shrinkage caused by hydration of the cementitious materials in the concrete.
2.1.2 Cementitious material
A general term for Portland cement and active mineral admixtures used to prepare
concrete.
2.1.3 Alternative bay construction method
A construction method, that divides an extra-long concrete block into several small
blocks for construction at intervals, then connects the several small blocks into a whole
after a short-term stress release. It relies on the tensile strength of the concrete to resist
the temperature shrinkage stress of the lower section.
2.1.4 Permanent deformation seam
Permanently reserved joints that divide buildings (structures) vertically, including
expansion joints and settlement joints.
t - Age of concrete;
Ts - Surface temperature of placed concrete block;
Tb(t) - Surface temperature of the placed concrete block at the age t;
Tbm(t), Tdm(t) - When the middle part of the placed concrete block reaches the highest
temperature, the temperature of the upper and lower surface layers of the block;
Tmax - The maximum temperature inside the placed concrete block;
Tmax(t) - The maximum temperature in the placed concrete block at the age t;
Tq - The average temperature of the atmosphere at which the concrete reaches its
maximum temperature;
T(t) - The adiabatic temperature rise of concrete at the age of t;
Ty(t) - The equivalent shrinkage temperature of concrete at the age of t;
Tw(t) - The expected stable temperature or final stable temperature of the placed
concrete block at the age of t;
ΔT1(t) - The temperature difference of core and surface of the concrete pouring block,
at the age of t;
ΔT2(t) - The comprehensive cooling difference of the concrete pouring block during
the cooling process, at the age of t;
ΔT1max(t) - The maximum possible temperature difference between inside and
outside after concrete pouring;
ΔT1i(t) - The increment of the temperature difference of core and surface of the
concrete pouring block, in the i-th calculation section at the age of t;
ΔT2i(t) - The increment of the comprehensive cooling difference of the concrete
pouring block, in the i-th calculation section at the age of t;
βµ - Heat release coefficient of solid in air;
βs - Total heat release coefficient of insulation material;
λ0 - Thermal conductivity of concrete;
λi - Thermal conductivity of the i-th layer of insulation material.
2.2.2 Quantitative geometric parameters
H - The thickness of the placed concrete block, which is the sum of the actual
4 Technical measures shall be taken to reduce the external constraints of mass
concrete in the design;
5 In the design, relevant testing requirements for temperature field and strain shall
be put forward based on the engineering conditions.
3.0.3 Before the construction of mass concrete, the temperature, temperature stress and
shrinkage stress of the placed concrete block shall be trial calculated; the peak value of
rising temperature of the placed concrete block, the control indicators of the
temperature difference of core and surface, the descending speed of temperature shall
be determined; corresponding technical measures for temperature control shall be
formulated.
3.0.4 The temperature control indicators for mass concrete construction shall comply
with the following requirements.
1 The temperature rise of the placed concrete block based on the temperature of
mixture placing to mold should not be greater than 50 °C;
2 The temperature difference of core and surface of the placed concrete block
(excluding the equivalent temperature of concrete shrinkage) should not be
greater than 25 °C;
3 The descending speed of temperature of the placed concrete block should not be
greater than 2.0 °C/d;
4 When removing the thermal insulation cover, the temperature difference between
the surface of the placed concrete block and the atmosphere shall not be greater
than 20 °C.
3.0.5 Before constructing mass concrete, it shall make construction preparations;
contact the local meteorological observatories and stations to understand recent
meteorological conditions. During winter construction, it shall also comply with the
relevant winter construction provisions for concrete.
3.0.6 Mass concrete construction shall adopt energy-saving, material-saving, water-
saving, land-saving, environmental protection measures. It shall comply with the
relevant provisions of the current national standard "Code for green construction of
building" GB/T 50905.
4 Materials, mix proportioning, production and
transportation
4.1 General requirements
4.1.1 In addition to meeting the design requirements for strength grade, durability,
impermeability, volume stability, the mass concrete's mix proportion design shall also
meet the requirements for mass concrete construction technology; it shall use materials
rationally and reduce the adiabatic temperature rise of concrete.
4.1.2 The preparation and transportation of mass concrete shall not only meet the
requirements of the concrete design strength grade, but also adjust the relevant
parameters of the ready-mixed concrete, according to the ready-mixed concrete supply
transportation distance, transportation equipment, supply capacity, material batch,
ambient temperature, etc.
4.2 Materials
4.2.1 The selection and quality of cement shall comply with the following requirements.
1 Cement shall comply with the relevant provisions of the current national standard
"Common Portland cement" GB 175.When other varieties are used, its
performance indicators shall comply with the relevant provisions of the current
national standards;
2 General Portland cement with low hydration heat shall be selected. The 3d heat of
hydration should not be greater than 250 kJ/kg; the 7d heat of hydration should
not be greater than 280 kJ/kg. When 52.5 strength grade cement is selected, the
7d heat of hydration should be less than 300 kJ/kg;
3 The entering temperature of cement in the mixing station should not be higher than
60 °C.
4.2.2 When cement used for mass concrete enters the site, it shall check the cement
variety, code, strength grade, packaging or bulk number, date of exit-factory, etc.;
it shall inspect the strength, stability, setting time, heat of hydration of the cement.
The inspection results shall comply with the relevant provisions of the current
national standard "Common Portland cement" GB 175.
4.2.3 The selection of aggregates, in addition to complying with the relevant provisions
of the current industry standard "Standard for technical requirements and test method
of sand and crushed stone (or gravel) for ordinary concrete" JGJ 52, shall also comply
with the following provisions.
1 The fine aggregate should be medium sand; the fineness modulus should be greater
materials; the amount of slag powder should not be greater than 40% of the
amount of cementing materials; the sum of the amount of fly ash and slag powder
should not be greater than 50% of the amount of cementing materials;
5 The water-binder ratio should not be greater than 0.45;
6 The sand rate should be 38% ~ 45%.
4.3.2 Before preparing concrete, it should conduct tests on technical parameters such as
adiabatic temperature rise, bleeding rate, pumpability, etc. that have an impact on the
control of cracks in mass concrete. If necessary, the mix proportioning design shall be
verified through trial pumping.
4.3.3 When determining the concrete mix proportioning, it shall propose the technical
measures for coarse and fine aggregate and mixing water during concrete preparation
and control of temperature of mixture placing to mold, based on the requirements of the
concrete adiabatic temperature rise and temperature control construction plan.
4.4 Production and transportation
4.4.1 The concrete preparation and transportation capacity shall meet the requirements
of concrete pouring technology. The quality of ready-mixed concrete shall comply with
the relevant provisions of the current national standard "Ready-mixed concrete" GB/T
14902.It shall also meet the technical requirements of construction technology for
slump loss, mold entry slump, temperature of mixture placing to mold, etc.
4.4.2 For ready-mixed concrete supplied at the same time for the same item work of
project, the cementitious materials, admixtures, mix proportions shall be consistent; the
preparation process and quality control level shall be basically the same.
4.4.3 Concrete mixer trucks shall be used to transport concrete mixture. The trucks shall
have sun protection, rainproof, heat preservation measures, according to the actual
conditions of the construction site.
4.4.4 The number of mixer trucks shall meet the requirements of concrete pouring
technology; the calculation method can be determined according to Appendix A of this
standard.
4.4.5 The delivery time of the mixer truck shall comply with the relevant provisions of
the current national standard "Ready-mixed concrete" GB/T 14902.
4.4.6 When adding admixtures for adjustment during transportation, the mixing truck
shall stir quickly; the mixing time shall not be less than 120 s.
4.4.7 During transportation and pouring, the performance of the mixture shall not be
adjusted by adding water.
4.4.8 When the slump loss or segregation is serious during transportation and the
working performance of the concrete mixture cannot be restored after taking measures,
it shall not be poured into the mold.
5 Construction
5.1 General requirements
5.1.1 The construction program of mass concrete construction shall include the
following main contents.
1 Calculation results of temperature stress and shrinkage stress of mass placed
concrete block;
2 Determination of main anti-cracking structural measures and temperature control
indicators during the construction stage;
3 Raw material selection, mix proportioning design, preparation, transportation plan;
4 Main construction equipment and general layout of the site;
5 Temperature control monitoring equipment and test layout diagram;
6 Pouring sequence and construction schedule;
7 Thermal insulation and moisturizing curing methods;
8 Emergency plans and emergency safeguard measures;
9 Construction measures for special locations and special climate conditions.
5.1.2 The temperature stress and shrinkage stress of mass concrete pouring block can
be determined according to Appendix B of this standard.
5.1.3 The thickness of the thermal insulation covering layer can be determined based
on Appendix C of this standard, according to the requirements of the temperature
control indicators.
5.1.4 Mass concrete construction should adopt overall layered or push-type continuous
pouring construction.
5.1.5 When horizontal construction joints are set up in mass concrete construction, the
location and interval time shall be determined according to design requirements,
temperature crack control requirements, concrete supply capacity, steel bar engineering
construction, embedded pipe installation and other factors.
responsibility system and a handover system shall be established.
5.3 Formwork
5.3.1 It shall check the bearing capacity, stiffness, overall stability of mass concrete
formwork and brackets; it shall design the thermal insulation structure based on
the maintenance methods used for mass concrete.
5.3.2 Safety and stability measures must be taken, during the installation, use, removal
of formwork and support systems.
5.3.3 For the vertical construction joints left behind by the post-casting strip or the
alternative bay construction method, materials such as steel mesh, wire mesh or quick
and easy closing mesh should be used for supporting. The vertical support system of
the post-casting strip should be separated from other parts.
5.3.4 The form removal time for mass concrete shall meet the strength requirements of
the concrete. When the formwork is used as part of the thermal insulation and curing
measures, the form removal time shall be determined according to the temperature
control requirements.
5.3.5 For mass concrete, the formwork removal time shall be appropriately delayed.
After removing the formwork, measures shall be taken to prevent cold current attacks,
sudden temperature drop, severe drying.
5.4 Placing
5.4.1 Mass concrete pouring shall comply with the following requirements.
1 The thickness of the concrete pouring layer shall be determined based on the depth
of action of the vibrator used and the workability of the concrete. It should be 300
mm ~ 500 mm for continuous overall pouring. Over-vibration and missing
vibration shall be avoided during vibration.
2 For overall layered continuous pouring or push-type continuous pouring, the
interval time shall be shortened; the second layer of concrete shall be poured
before the initial setting of the previous layer of concrete. The interval time
between layers shall not be greater than the initial setting time of concrete. The
initial setting time of concrete shall be determined by testing. When the interval
time between layers exceeds the initial setting time of concrete, the layers shall
be treated as construction joints.
3 Concrete pouring shall be continuous and orderly; construction joints should be
reduced.
4 Concrete should adopt pumping method and secondary vibration technology.
5.4.2 When layered intermittent pouring of concrete is adopted, the treatment of
horizontal construction joints shall comply with the following requirements.
1 On the surface of hardened concrete, the surface float slurry, loose stones, weak
concrete layer shall be removed;
2 Before pouring the upper layer of concrete, the dirt on the concrete surface shall
be washed away with clean water and fully moistened; however, there shall be no
accumulation of water;
3 The newly poured concrete shall be vibrated and compacted; it shall be closely
combined with the previously poured concrete.
5.4.3 Where there are waterproofing requirements for the construction joints connecting
the mass concrete floor and side walls, steel plate water stops and other treatment
measures shall be taken.
5.4.4 During the mass concrete pouring process, measures shall be taken to prevent the
displacement and deformation of stressed steel bars, positioning bars, embedded parts,
etc.; the bleeding on the concrete surface shall be removed in a timely manner.
5.4.5 The mass concrete pouring surface shall be troweled multiple times in a timely
manner.
5.5 Curing
5.5.1 Mass concrete shall be cured with thermal insulation and moisturizing. After each
concrete placing, in addition to regular curing as ordinary concrete, thermal insulation
curing shall comply with the following requirements.
1 A designated person shall be responsible for the thermal insulation curing work;
take the test record;
2 The duration of moisturizing and curing should not be less than 14 days. It shall
check the integrity of the plastic film or curing agent coating frequently; keep the
concrete surface moist;
3 The thermal insulation covering shall be removed step by step in layers. When the
maximum temperature difference between the concrete surface temperature and
the environment is less than 20 °C, it can be completely removed.
5.5.2 After the concrete placing is finished, it should carry out covering or spray curing
immediately before initial setting.
5.7 Sampling in site
5.7.1 When mass concrete no larger than 1000 m3 with the same mix proportioning is
placed continuously at one time, the on-site sampling number of concrete strength test
specimens shall not be less than 10 groups.
5.7.2 When mass concrete of 1000 m3 ~ 5000 m3 with the same mix proportioning is
placed continuously at one time, for the concrete exceeding 1000 m3, it shall take not
less one group of samples for each additional 500 m3; OR take one group of samples if
it is not more than 500 m3.
5.7.3 When mass concrete larger than 5000 m3 with the same mix proportioning is
poured continuously at one time, for the concrete exceeding 5000 m3, it shall take not
less one group of samples for each additional 1000 m3; OR take one group of samples
if it is not more than 1000 m3.
6 Temperature monitor and control
6.0.1 The temperature difference of core and surface of the mass concrete, the
descending speed of temperature, the ambient temperature shall be tested not less than
4 times every day and night after the concrete is placed; the temperature of mixture
placing to mold shall be measured not less than 2 times per shift.
6.0.2 The layout of monitoring points in the mass placed concrete block shall reflect the
maximum temperature rise, the temperature difference of core and surface, the
descending speed of temperature, the ambient temperature in the placed concrete block.
The following layout methods can be adopted.
1 The half axis of the plane symmetry axis of the placed concrete block can be
selected in the test area. The monitoring points in the test area shall be arranged
in layers according to the plane;
2 In the test area, the location and number of monitoring points can be determined
according to the distribution of the temperature field in the placed concrete block
and the temperature control requirements;
3 On each test axis, there should be no less than 4 monitoring points, which shall be
arranged according to the plane size of the structure;
4 Along the thickness direction of the placed concrete block, at least the surface layer,
bottom layer, core temperature measuring points shall be arranged; the distance
between measuring points should not be greater than 500 mm;
5 The thermal insulation curing effect and the number of ambient temperature
monitoring points shall be determined according to specific needs;
6 The surface temperature of the placed concrete blocks should be the temperature
50 mm within the surface of the placed concrete block;
7 The temperature of the bottom layer of the placed concrete block should be the
temperature 50 mm above the bottom surface of the placed concrete block.
6.0.3 Strain test should be carried out according to project needs.
6.0.4 The selection of test components shall comply with the following requirements.
1 In a 25 °C environment, the temperature measurement error shall not be greater
than 0.3 °C;
2 The temperature test range shall be -30 °C ~ 120 °C;
3 The test resolution of strain test components shall not be greater than 5 με;
4 The strain test range shall meet the requirements of -1000 με ~ 1000 με;
5 The insulation resistance of the test element shall be greater than 500 MΩ.
6.0.5 The installation and protection of temperature testing components shall comply
with the following requirements.
1 Before installation, the test components shall be soaked 1 m underwater for 24
hours without damage;
2 The test components shall be firmly fixed and isolated from the structural steel
bars and the metal body of the fixing frame;
3 The lead wires of test components should be arranged in a centralized manner,
marked and protected along the wiring direction;
4 Protective measures shall be taken around the test components. The temperature
test components and their lead wires must not be directly impacted or touched
during batching and vibration.
6.0.6 During the test process, the temperature change curve of each point and the cross-
section temperature distribution curve shall be drawn.
6.0.7 When abnormal monitoring results are found, it shall sound the alarm immediately
and take corresponding measures.
6.0.8 Temperature control measures can be adjusted in real time based on the following
principles or methods and combined with monitoring data.
1 Control the temperature of the concrete leaving the mixer and regulate the
temperature of mixture placing to mold within a suitable range;
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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