 Classification  Features in Influencing Concrete  Fine Aggregate-Sand  Coarse Aggregate-Gravel Aggregate

Coarse Aggregate Definition Definition Definition Classification Classification Classification Requirements of Aggregate Requirements of Aggregate Requirements of Aggregate Requirements of Aggregate  Impurities  Particle Shape and Surface Texture  Particle Size Gradation  Type of Particle Size Gradation  Maximum Size  Aggregate Strength

It refers to the aggregate larger than 5mm Must be in agreement with GB/T (JGJ53-92)

Aggregate Primary Gravel Scree According to shape of primary coarse aggregate, it can be divided into gravel and scree. According to shape of primary coarse aggregate, it can be divided into gravel and scree. Gravel is the widely used primary coarse aggregate. Gravel is the widely used primary coarse aggregate. Classification

 Ⅰ : I n the concrete the strength grade is more than C60 ；  Ⅱ : I n the concrete the strength grade is between C30-C60; Aggregate Technical requirement Ⅲ Ⅱ Ⅰ  Ⅲ : I n the concrete the strength grade is less than C30. By quality, there are three types: Ⅰ, Ⅱ and Ⅲ Classification

 Impurities  Particle Shape and Surface Texture  Particle Size Gradation  Type of Particle Size Gradation  Maximum Size  Aggregate Strength

 Clay content, clod content, and the content of needle shape particles and slice shape particles must be in agreement with GB/T (JGJ52-92). Impurities Limits of type and content Fig4.2.1Needle and Slice Shape Particles

 D etails will be introduced later in durability of concrete.  If there is potential danger, the alkali content should be less than 0.6%.  A special test is needed when we used the admixture containing potassium and sodium. Alkali-aggregate Reaction

 The particle shape and surface texture are the same with that of the sand. Particle Shape and Surface Texture Particle Size Gradation  T he parameter is the same with the sand in the test method of gradation and the calculation.  Only differs in the size of sieve pore and the requirements of gradation.

 S tandard screen size: 2.5 、 5.0 、 10 、 16 、 20 、 25 、 31.5 、 40 、 50 、 63 、 80 、 100 and so on. 2.5 、 5.0 、 10 、 16 、 20 、 25 、 31.5 、 40 、 50 、 63 、 80 、 100 and so on. Particle Size Gradation Fig Screen Instrument

Type of Particle Size Gradation Particle Size Gradation Sequent Grading Discontinuous Gradation Single Gradation There are three types of particle size gradation sequent grading, discontinuous gradation and single gradation.

Sequent Gradation  Every gradation of gravel accounts for a certain proportion from the small to the big so that the workability is excellent and it is not easy to form layers. Discontinuous Gradation  Rid some particles of some gradation to reduce porosity; separate out easily so that high strength concrete or dry concrete can be produced with pounding. Single Gradation  It is used to form sequent gradation or mix with coarse aggregate in continuous gradation, but the porosity is bigger and easier to be separated out when alone.

Maximum Size: Maximum size refers to the upper line of nominal gradation of gravel. For example:5 ～ 20 is a range of nominal gradation, 20mm is the upper line of nominal gradation. 5 ～ 20 limit of nominal gradation Upper limit of nominal gradation Maximum Size

Maximum Size Economy Quantities of cement Specific Surface area Maximum Size (D max ) can be decided according to the economy, Structure Limit and ConstructionMaximum Size (D max ) can be decided according to the economy, Structure Limit and Construction D max, smaller the specific surface, Less the quantities, higher the economy Ⅰ. Economy Larger the D max, smaller the specific surface, Less the quantities, higher the economy Maximum Size

Ⅱ. Structure Limit ≯ 1/4 minimum size of section ≯ 3/4minimum clear distance of bar =1/2 thickness of solid floor and ≯ 50mm According to structure standard, the Dmax should meet the following requirements: Dmax ≯ 1/4 minimum size of section Dmax ≯ 3/4minimum clear distance of bar Dmax =1/2 thickness of solid floor and ≯ 50mm Maximum Size

Ⅲ. Construction  D max must meet the requirements of the construction.  Segregation, breakage of vane, walling up the tube of pump and vibration are easily produced in the process of mixing, transporting and vibrating, if maximum size is too large. Maximum Size

 There are two methods to measure the strength of the aggregate strength: cubic strength of rock and crushing index of gravel.  Cubic strength of rock The compressive strength of the cube is measured in saturated water. Aggregate Strength 5cm×5cm×5cm Fig4.2.3 Sketch map to measure cubic strength Cubic strength of rock

 For ordinary concrete: Aggregate strength ≮ 1.5 f cu  For HSC: Aggregate strength ≮ 2.0 f cu  Also select the strength of rock according to the rocks types (list in Tab) Aggregate Strength Rocks RocksStrength Igneous rock ≮ 80 MPa Metamorp hic rock ≮ 60 MPa Aqueous rock ≮ 30 MPa Tab4.2.6 Aggregate Strength of different types different types

Method: Put the gravel with the diameter of 10-20mm into the standard cylinder three times,press them to 200kN and sift them in 2.5mm sieve. Crushing index = m 0 —mass of dry gravel before crushing m 1 —mass of dry gravel after crushing and sifting Press Sife Aggregate Strength Crushing Index of Gravel Fig Sketch map to Crushing Index measure Crushing Index

石子压碎指标试验录像

Crushing Index Types of rock Concrete strength grade Gravel crushing index （ % ） Aqueous rock C55 ～ C40 ≤C35 ≤10 ≤16 Metamorphic rock or plutonic igneous rock C55 ～ C40 ≤C35 ≤12 ≤20 Igneous rock C55 ～ C40 ≤C35 ≤13 ≤30 Crushing Index of Gravelof different Tab Crushing Index of Gravel of different types Crushing index of gravel or scree are listed in Tab4.2.7 and Tab4.2.8 Crushing index of gravel or scree are listed in Tab4.2.7 and Tab4.2.8

Tab Crushing Index of Scree (GB/T ) Concrete strength grade C55-C40≤C35 Crushing index (%) ≤12≤16 Crushing Index

What kind of methods should be used  What kind of methods should be used  Cubic strength of rock  Crushing Index of Gravel  Cubic strength of rock is used for strength of high strength concrete.  Cubic strength of rock should be accorded with when it’s disputable between the two methods.