1 General provisions
1.0.1 This standard is formulated with a view to implementing the national technical and economic policies, ensuring the engineering quality, and achieving advanced technology, reasonable process, resource saving and environmental protection in the construction of mass concrete.
1.0.2 This standard is applicable to the construction of mass concrete in concrete structure, but is not applicable to the construction of roller-compacted concrete (RCC) and hydraulic mass concrete engineering, etc.
1.0.3 In addition to this standard, the construction of mass concrete shall also comply with those stipulated in the current relevant standards of the nation.
2 Terms and symbols
2.1 Terms
2.1.1 mass concrete
large volume of concrete in concrete structure body with a minimum size of not less than 1m, or concrete expected to have harmful crack due to temperature change and shrinkage caused by hydration of cementitious material in the concrete
2.1.2 cementitious material
a generic term for Portland cement and active mineral admixture for preparation of concrete
2.1.3 alternative bay construction method
a construction method that the ultra-long concrete block is divided into several small blocks, construction of these small blocks is hereby carried out alternatively to allow stress release for a short term, and then they are connected as a whole, and the connected concrete block can resist the temperature shrinkage stress of the next section relying on the tensile strength of concrete
2.1.4 permanent deformation seam
seam reserved permanently to vertically divide the building (structure), including expansion joint and settlement joint
2.1.5 vertical construction seam
seam reserved vertically at appropriate position when concrete cannot be continuously placed and the placing pause time may exceed the initial setting time of concrete
2.1.6 horizontal construction seam
seam reserved horizontally at appropriate position when concrete cannot be continuously placed and the placing pause time is possible to exceed the initial setting time of concrete
2.1.7 thermal stress
stress generated inside the concrete when the temperature deformation of the concrete is constrained
2.1.8 shrinkage stress
stress generated inside the concrete when the shrinkage deformation of the concrete is constrained
2.1.9 peak value of rising temperature
the maximum temperature rise value inside the placed concrete body
2.1.10 temperature difference of core and surface
the difference between the maximum temperature inside the placed concrete body and the temperature at a position 50mm inside its external surface
2.1.11 thickness weighted mean temperature
value obtained by weighted averaging the temperature value of each measuring point according to the weight of the length to thickness of the section represented by each temperature measuring point of the test spot
2.1.12 descending speed of temperature
decrease of the thickness weighted mean temperature within 24h after the internal temperature of placed concrete body reaches the peak value of rising temperature under heat dissipation condition
2.1.13 temperature of mixture placing to mold
temperature at which the concrete mixture is placed to the mold
2.1.14 harmful crack
crack that affects structural safety or use functions
2.1.15 adiabatic temperature rise
temperature rise value at a certain time inside the placed concrete body in an adiabatic state
2.1.16 binder paste content
ratio of the paste amount of cementitious material in the concrete to the total amount of concrete
2.1.17 temperature field
spatial and temporal distribution of concrete temperature
2.2 Symbols
2.2.1 Temperature and material performance
a——the thermal diffusivity of concrete;
C——the specific heat capacity of concrete;
Cx——the horizontal deformation stiffness of external restraint medium (foundation or old concrete);
E0——the elastic modulus of concrete;
E(t)——the elastic modulus of concrete at an age of t;
Ei(t)——the elastic modulus of concrete at an age of t in the ith calculation section;
ftk(t)——the standard value of tensile strength of concrete at an age of t;
Kb, K1, K2——the corrected value of heat transfer coefficient for the surface thermal insulation layer of placed concrete body;
m——the coefficient related to cement type, placing temperature, etc.;
Q——the total hydration heat of cementitious material;
Q0——the total hydration heat of cement;
Qt——the cumulative hydration heat at an age of t;
Rs——the total thermal resistance of thermal insulation layer;
t——the age of concrete;
Ts——the surface temperature of placed concrete body;
Tb(t)——the surface layer temperature in the placed concrete body at an age of t;
Tbm(t), Tdm(t)——respectively the temperature of the upper and lower surface layers of placed concrete body when the maximum temperature occurs at the middle part;
Tmax——the maximum temperature in the placed concrete body;
Tmax(t)——the maximum temperature in the placed concrete body at an age of t;
Tq——the average atmospheric temperature when the concrete reaches the maximum temperature;
T(t)——the adiabatic temperature rise of concrete at an age of t;
Ty(t)——the shrinkage equivalent temperature of concrete at an age of t;
Tw(t)——the expected stable temperature or final stable temperature of placed concrete body at an age of t;
ΔT1(t)——the temperature difference of core and surface of the placed concrete body at an age of t;
ΔT2(t)——the comprehensive temperature drop difference of placed concrete body during temperature descending at an age of t;
ΔT1max(t)——the maximum temperature difference of core and surface that may occur after concrete is placed;
ΔT1i(t)——the increment of the temperature difference of core and surface of placed concrete body at an age of t in the ith calculation section;
ΔT2i(t)——the increment of the comprehensive temperature drop difference of placed concrete body at an age of t in the ith calculation section;
βμ——the heat release coefficient of solids in air;
βs——the total heat release coefficient of the thermal insulation material;
λ0——the thermal conductivity of concrete;
λi——the heat conductivity coefficient of the ith layer of thermal insulation material.
2.2.2 Quantitative and geometric parameters
H——the thickness of the placed concrete body, which is the sum of the actual thickness of the placed body and the virtual thickness of thermal insulation layer converted into concrete;
h——the actual thickness of concrete;
h′——the virtual thickness of concrete;
L——the round-trip distance of concrete truck mixer;
N——the number of concrete truck mixers;
Q1——the actual average output of each concrete pump;
Qmax——the maximum output of each concrete pump;
S——the average driving speed of concrete truck mixer;
Tt——the total stop time of each concrete truck mixer;
V——the capacity of each concrete truck mixer;
W——the consumption of cementitious material per cubic meter of concrete;
α1——the piping condition coefficient;
δ——the thickness of thermal insulation layer on the surface of concrete;
δi————the thickness of the ith layer of thermal insulation material.
2.2.3 Calculation parameters and others
H(t, τ)——the relaxation coefficient of the restraint stress, which is generated at an age of τ, after reaching the age of t;
K——the crack resistance safety coefficient;
k——the hydration heat adjustment coefficient of admixture under different mixing amount;
k1, k2——respectively the hydration heat adjustment coefficient corresponding to the mixing amount of flyash and slag powder;
M1, M2…M11——the correction coefficients of concrete shrinkage deformation under different conditions;
Ri(t)——the restraint coefficient of external restraint in the ith calculation section at an age of t;
n——the constant, depending on factors such as cement type and specific surface area;
——the reciprocal of the hydraulic radius;
α——the coefficient of linear expansion of concrete;
β——the correction coefficient for elastic modulus by the admixture in concrete;
β1, β2——respectively the correction coefficient for elastic modulus corresponding to the mixing amount of flyash and slag powder in concrete;
ρ——the mass density of concrete;
ε_y^0——the relative deformation value of the final shrinkage of concrete under standard test conditions;
εy(t)——the relative deformation value caused by shrinkage of concrete at an age of t;
σx(t)——the tensile stress generated under external restraints due to the comprehensive temperature drop difference at an age of t;
σz(t)——the cumulative value of the self-restraint tensile stress generated due to the temperature difference of core and surface of placed concrete body at an age of t;
η——the operation efficiency;
σzmax——the maximum self-restraint stress.
3 Basic requirements
3.0.1 For the construction of mass concrete, construction organization design or construction technical scheme shall be prepared, and technical measures for environmental protection and safe construction shall be provided.
3.0.2 The construction of mass concrete shall meet the following requirements:
1 The design strength grade of mass concrete should be C25~C50, and the strength of concrete at an age of 60d or 90d may be used as the basis for concrete mix proportioning design, concrete strength evaluation and engineering acceptance;
2 The structural reinforcement of mass concrete shall meet the bearing capacity and detailing requirements of the structure, and the constructional steel bar for temperature and shrinkage control shall also be applied in combination with the construction method of mass concrete;
3 When the mass concrete is placed on the rock foundation, a sliding layer should be provided on the concrete cushion;
4 Technical measures shall be taken to reduce the external restraints of mass concrete;
5 The relevant test requirements for temperature field and strain shall be proposed in design according to the engineering conditions.
3.0.3 Before the construction of mass concrete, the temperature, thermal stress and shrinkage stress of the placed concrete body shall be calculated, the control indexes for the peak value of rising temperature, temperature difference of core and surface and descending speed of temperature of the placed concrete body shall be determined, and corresponding temperature control technical measures shall be formulated.
3.0.4 The temperature control index for the construction of mass concrete shall meet the following requirements:
1 The temperature rise value of placed concrete body on the basis of temperature of mixture placing to mold should not be greater than 50℃;
2 The temperature difference of core and surface of the placed concrete body (excluding the shrinkage equivalent temperature of concrete) should not be greater than 25℃;
3 The descending speed of temperature of the placed concrete body should not be greater than 2.0℃/d.
4 When the thermal insulation cladding is removed, the difference between the surface temperature of placed concrete body and atmospheric temperature shall not be greater than 20℃.
3.0.5 Before the construction of mass concrete, construction preparation shall be done, and local meteorological station shall be contacted to grasp the recent meteorological conditions. In the winter construction, the construction of mass concrete shall also comply with the relevant requirements for winter construction of concrete.
3.0.6 The construction of mass concrete shall be provided with the energy-saving, material-saving, water-saving and land-saving and environmental protection measures, and shall meet the relevant requirements of the current national standard GB/T 50905 Code for green construction of building.
4 Materials, mix proportioning, production and transportation
4.1 General requirements
4.1.1 In addition to the design requirements such as strength grade, durability, impermeability and volume stability, mix proportioning design of mass concrete shall also meet the construction technology requirements of mass concrete, and it’s also required to use materials reasonably and reduce the adiabatic temperature rise of concrete.
4.1.2 As for preparation and transportation of mass concrete, in addition to meeting the requirements of concrete design strength grade, the relevant parameters of ready-mixed concrete shall be adjusted according to its transportation distance, transportation equipment, supply capacity, material batch No. and ambient temperature.
4.2 Materials
4.2.1 Selection and quality of concrete shall be in accordance with the following requirements:
1 Cement shall conform to the relevant requirements of the current national standard GB 175 Common Portland Cement. When other types of cement are used, the performance indexes shall conform to the relevant current standards of the nation;
2 It is required to use the common Portland cement with low hydration heat; 3d hydration heat should not be greater than 250kJ/kg and 7d hydration heat should not be greater than 280kJ/kg; when the cement of strength grade 52.5 is used, 7d hydration heat should be less than 300kJ/ Kg;
3 The temperature of cement into machine at the mixing plant should not be higher than 60℃.
4.2.2 The type, code, strength grade, packaging or bulking No., ex-factory date, etc. shall be checked when the cement to be used for mass concrete enter the site; the strength, stability, setting time and hydration heat of such cement shall also be inspected, and the inspection results shall meet the relevant requirements of the current national standard GB 175 Common Portland Cement.
4.2.3 In addition to the relevant requirements specified in the current professional standard JGJ 52 Standard for technical requirements and test method of sand and crushed stone (or gravel) for ordinary concrete, the selection of aggregates shall also meet the following requirements:
1 Medium sand should be adopted for fine aggregate whose fineness modulus should be greater than 2.3 and silt content shall not exceed 3%;
2 For coarse aggregate, the particle size should be 5.0mm~31.5mm, it shall be continuously graded, and the silt content shall not exceed 1%;
3 It is required to use non-alkali reactive coarse aggregate;
4 When non-pumping construction is adopted, the particle size of the coarse aggregate may be appropriately increased.
4.2.4 The quality of flyash and ground granulated blast furnace slag shall meet the relevant requirements of the current national standards GB/T 1596 Fly ash used for cement and concrete and GB/T 18046 Ground granulated blast furnace slag used for cement, mortar and concrete.
4.2.5 The quality and application technology of admixture in the concrete shall meet relevant requirements of the current national standards GB 8076 Concrete admixtures and GB 50119 Code for utility technical of concrete admixture.
4.2.6 In addition to the relevant requirements of 4.2.5, the selection of admixture shall also meet the following requirements:
1 The type and mixing amount of admixture shall be determined according to the material test;
2 It is advisable to provide the influence coefficients of admixture on the shrinkage of the hardened concrete;
3 For mass concrete with high durability requirements or in cold areas, air-entraining agent or air-entraining water-reducing agent should be used.
4.2.7 The quality of water for mixing the concrete shall conform to the current professional standard JGJ 63 Standard of water for concrete.
4.3 Mix proportioning design
4.3.1 In addition to the current professional standard JGJ 55 Specification for mix proportion design of ordinary concrete, the mix proportioning design of mass concrete shall also meet the following requirements:
1 When 60d or 90d concrete strength acceptance index are used, it shall be used as the design basis for concrete mix proportioning;
2 The slump of concrete mixture should not be greater than 180mm;
3 The amount of mixing water should not exceed 170kg/m3;
4 The mixing amount of flyash, that of slag powder and the sum of both should not be greater than 50%, 40% and 50% of the consumption of cementitious material respectively;
5 The water-cementitious material ratio should not be greater than 0.45;
6 The sand percentage should be 38%~45%.
4.3.2 Before the preparation of concrete, it is advisable to carry out the tests of technical parameters that affect the crack control of mass concrete, such as adiabatic temperature rise, bleeding rate and pumpability. If necessary, the mix proportioning design shall be verified by trial pumping.
4.3.3 During the determination of the mix proportioning of concrete, the technical measures for coarse/fine aggregates and mixing water as well as control of temperature of mixture placing to mold during concrete preparation should be proposed according to the requirements of construction scheme in terms of concrete adiabatic temperature rise and temperature control.
4.4 Preparation and transportation
4.4.1 The capacities of concrete preparation and transportation shall meet the requirements of concrete placing technology. The quality of ready-mixed concrete shall comply with the relevant requirements of the current national standard GB/T 14902 Ready-mixed concrete, and shall meet the technical requirements of construction process for slump loss and slump of mixture placing to mold, temperature of mixture placing to mold, etc.
4.4.2 For ready-mixed concrete for subitems of the same works, the content of cementitious materials & admixtures and mix proportioning shall be consistent, and the preparation process and quality control level shall be basically the same.
4.4.3 Concrete truck mixer shall be used for transportation of concrete mixture. The trucks shall be provided with sun protection, rain protection and thermal insulation measures according to the actual conditions of the construction site.
4.4.4 The quantity of truck mixers shall meet the requirements of concrete placing technology, and the calculation method may be determined in accordance with Annex A.
4.4.5 The time of transportation by truck mixers shall meet the relevant requirements of the current national standard GB/T 14902 Ready-mixed concrete.
4.4.6 During the adjustment through supplementation with admixtures in the transportation process, the truck mixers shall stir quickly for at least 120s.
4.4.7 During the transportation and placing process, the performance shall be adjusted in methods except for adding water to the mixture.
4.4.8 When the slump loss or segregation is severe during transportation, the concrete mixture shall not be placed into the mold after it fails to restore its working performance using certain measures.
1 General provisions
2 Terms and symbols
2.1 Terms
2.2 Symbols
3 Basic requirements
4 Materials, mix proportioning, production and transportation
4.1 General requirements
4.2 Materials
4.3 Mix proportioning design
4.4 Preparation and transportation
5 Construction
5.1 General requirements
5.2 Technical preparation
5.3 Formwork
5.4 Concrete placing
5.5 Concrete curing
5.6 Construction in special climate
5.7 Site sampling
6 Temperature monitoring and control
Annex A Calculation for output of concrete pump and number of truck mixers
Annex B Calculation for thermal stress and shrinkage stress during construction of placed mass concrete body
Annex C Calculation for the thickness of surface thermal insulation layer of placed mass concrete body
Explanation of wording in this standard
List of quoted standards
