1 INTRODUCTION A revision of NZS 3121 Water and aggregate for concrete was published in 2015. The revision was comprehensive and covered the following areas. This Technical Note will cover aggregate selection and aggregate testing. Three NZRMCA Technical Notes cover other aspects of NZS 3121. • Technical Note 1 - Precautions to be taken to determine the potential alkali reactivity of aggregate in accordance with CCANZ TR 3 • Technical Note 2 - Water for use in concrete including use of recycled wash water • Technical Note 8 - Determining the chloride content of concrete • This Technical Note 3 – Water and aggregate for concrete - Harmful Materials - Recycled materials used as aggregate in concrete - Properties and control testing of coarse aggregate and of sand - Testing for potentially detrimental fine dust or clay like materials in sand HARMFUL MATERIALS The aggregate supplier is responsible for eliminating harmful materials from concrete aggregate and the Plant Engineer needs to be satisfied that sufficient controls are in place. ASTM C1602M - 12 Standard specification for mixing water used in the production of hydraulic cement concrete: Annex 1 provides a procedure for comparing 7 & 28 day results of a trial concrete with an unproven aggregate, against a control concrete with an aggregate of known acceptable performance. Compressive strengths of the trial concrete shall be no less than 90% of the control concrete. The use of recycled materials has the potential to introduce harmful materials into concrete. CCANZ TR 14 Best practice guide for the use of recycled aggregates and materials in new concrete provides composition limitations in Table 7 on materials (Masonry, Fines, Lightweight material, Asphalt or Glass, Plastic, Wood) recycled from demolition waste concrete for use as ‘Recycled Coarse Aggregate’ in concrete. TR 14 Table 9 suggests control limits on the fraction of recycled material based on concrete specified strength. By restricting the % recycled material at a given strength, the influence of harmful materials will be less. ‘Recovered Aggregate’ obtained from washing out the coarse aggregate fraction from leftover fresh concrete, or ‘Leftover Concrete Aggregate’ where fresh returned concrete is allowed to harden, and then crushed, do not have the potential to contain harmful materials to the extent that ‘Recycled Concrete Aggregate’ does, as the recycled aggregate is from an unknown source. COARSE AGGREGATE With sources of natural river run concrete aggregates diminishing, quarried aggregates are now used in the majority of ready mix plants and the risks associated with the use of more marginal aggregates dictate a more comprehensive testing programme. Different aggregates require different assessment methods and control limits. Properties of coarse aggregate can be termed ‘Production’ properties or ‘Source’ properties. Production properties change on a daily basis due to manufacturing systems. Source properties change on a less regular basis and a related to the source rock and changes in the location of the rock extraction. Mandatory testing and additional testing are given in NZS 3121. Control limits are also given. Additional testing may be specified by the Plant Engineer appropriate to the source and type of aggregate supplied. CONCRETE NZ READYMIX TECHNICAL NOTE 3 WATER AND AGGREGATE FOR CONCRETE JUNE 2018
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INTRODUCTIONA revision of NZS 3121 Water and aggregate for concrete was published in 2015. The revision was comprehensive and covered the following areas. This Technical Note will cover aggregate selection and aggregate testing. Three NZRMCA Technical Notes cover other aspects of NZS 3121.
• Technical Note 1 - Precautions to be taken to determine the potential alkali reactivity of aggregate in accordance with CCANZ TR 3
• Technical Note 2 - Water for use in concrete including use of recycled wash water
• Technical Note 8 - Determining the chloride content of concrete
• This Technical Note 3 – Water and aggregate for concrete
- Harmful Materials
- Recycled materials used as aggregate in concrete
- Properties and control testing of coarse aggregate and of sand
- Testingforpotentiallydetrimentalfinedustorclaylikematerialsinsand
HARMFUL MATERIALSThe aggregate supplier is responsible for eliminating harmful materials from concrete aggregate and the Plant Engineerneedstobesatisfiedthatsufficientcontrolsareinplace.
ASTM C1602M - 12 Standard specification for mixing water used in the production of hydraulic cement concrete: Annex 1 provides a procedure for comparing 7 & 28 day results of a trial concrete with an unproven aggregate, against a control concrete with an aggregate of known acceptable performance. Compressive strengths of the trial concrete shall be no less than 90% of the control concrete.
The use of recycled materials has the potential to introduce harmful materials into concrete. CCANZ TR 14 Best practice guide for the use of recycled aggregates and materials in new concrete provides composition limitations in Table 7 on materials (Masonry, Fines, Lightweight material, Asphalt or Glass, Plastic, Wood) recycled from demolition waste concrete for use as ‘Recycled Coarse Aggregate’ in concrete. TR 14 Table 9 suggests control limitsonthefractionofrecycledmaterialbasedonconcretespecifiedstrength.Byrestrictingthe%recycledmaterialatagivenstrength,theinfluenceofharmfulmaterialswillbeless.
‘Recovered Aggregate’ obtained from washing out the coarse aggregate fraction from leftover fresh concrete, or ‘Leftover Concrete Aggregate’ where fresh returned concrete is allowed to harden, and then crushed, do not have the potential to contain harmful materials to the extent that ‘Recycled Concrete Aggregate’ does, as the recycled aggregate is from an unknown source.
COARSE AGGREGATEWith sources of natural river run concrete aggregates diminishing, quarried aggregates are now used in the majority of ready mix plants and the risks associated with the use of more marginal aggregates dictate a more comprehensivetestingprogramme.Differentaggregatesrequiredifferentassessmentmethodsandcontrollimits.
Properties of coarse aggregate can be termed ‘Production’ properties or ‘Source’ properties. Production properties change on a daily basis due to manufacturing systems. Source properties change on a less regular basis and a related to the source rock and changes in the location of the rock extraction. Mandatory testing and additionaltestingaregiveninNZS3121.Controllimitsarealsogiven.AdditionaltestingmaybespecifiedbythePlant Engineer appropriate to the source and type of aggregate supplied.
CONCRETE NZ READYMIX TECHNICAL NOTE 3WATER AND AGGREGATE FOR CONCRETE JUNE 2018
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PRODUCTION PROPERTIES OF COARSE AGGREGATE
The grading variation is monitored by the % passing the intermediate sieve, and also the cleanness values, are mandatory tests, as have historically been used. Four additional tests are given as follows – Density and Absorption, Flakiness Index, Misshapen Particles and Unit Mass.
SOURCE PROPERTIES OF COARSE AGGREGATE
The Plant Engineer in conjunction with the aggregate supplier shall request a testing regime at the start of supply or a major change of rock source. The weathering quality index is a mandatory test and Crushing Resistance, Wet and Dry Strength Variation and Weak Particles in Coarse Aggregate are additional source tests.
SANDWith quarried aggregates now used in the majority of ready mix plants, the risks associated with the use of more marginal aggregates, establishing and controlling cleanness of sand, particularly clay content is important. This areaiscoveredundertheStandardas‘qualityoffines’.
NZS3121coversnaturalsands,crushedaggregatefines,manufacturedsandswhicharepurposemadecrushedsands, or a blended sand being any combination of these three sand types.
PRODUCTION PROPERTIES OF SAND
Thegradingtestbasedonmonitoringfinenessmodulusandalsothe%bymassretainedonthe4.75mmsieve,as have historically been used, are mandatory production tests for sand. Flow time and Density and absorption are additional tests. Figure 1 in the Standard, reproduced below, illustrates the characteristics of a sand, or test sandblend,dependingonflowtimeandvoidscontent.
FLOW TIME VERSUS PER CENT VOIDS PLOT ILLUSTRATING THE CHARACTERISTICS OF SAND
CONCRETE NZ READYMIX TECHNICAL NOTE 3WATER AND AGGREGATE FOR CONCRETE JUNE 2018
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CONCRETE NZ READYMIX TECHNICAL NOTE 3WATER AND AGGREGATE FOR CONCRETE JUNE 2018
QUALITY OF FINESTheperformanceofaconcretesandorblendofsandsisaffectedbyanydustorclaylikematerialpresentinthesand. Five tests are given in NZS 3121 for the Plant Engineer to select the most appropriate test or tests and pass/fail criteria for a particular sand or sand combination. These are Sand Equivalent, Clay and Silt Content, Weighted Clay Index, Clay Index and Petrographic Analysis.
The Sand Equivalent test does not have a control limit covering all sands. Indicative values are 40 – 60 for manufacturedsands,andupto80forcleannaturalsands.Thetestisnotgoodatdifferentiatingbetweenclayfinesandultrafine-rock.TheWeightedClayIndexandClayIndexareeffectiveatindicatingthequantityofdetrimentalfinespresentandthepresenceofswellingclaymineralsrespectively.
TEST FREQUENCY
The grading test frequency for aggregate and sand is given in NZS 3121 Table 6 and 8 respectively. It is based onaninitialcompliancesamplingrate,movingtoalowerconfirmationsamplingratebasedonmeetingpass/failcriteria in the initial testing. Cleanness of aggregate shall be tested twice a month.
All additional Production property and Source property tests shall be carried out at a frequency determined by the Plant Engineer.
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