With three new branded sections relating to concrete, we have provided a brief overview article describing common concrete terminology and related specification considerations as well as terminology relating to Firth's new concrete sections.
Ready-Mixed Concrete
Ready-Mixed Concrete is produced at a batching plant which measures within permitted tolerances:
- Portland cement, sand, aggregates by weight.
- Water by weight or volume.
- Admixtures (if used) by sight glass or pulse meter.
These materials are then mixed in a concrete mixer in the plant or in a truck mixer at the batching plant. Once mixing is complete the resulting Ready-Mixed Concrete is then delivered to site in a plastic state. This process of producing Ready-Mixed Concrete is used for the supply of Normal Concrete and Special Concrete. Prescribed Mix Concrete is not a Ready-Mixed Concrete as it is batched by volume not weight.
Specification of Concrete
For the specification and manufacture of concrete NZS 3109 Concrete construction requires Normal Concrete, Special Concrete and Prescribed Mix Concrete in accordance with NZS 3104 Specification for Concrete production together with:
- The specified compressive strength
- Nominal maximum aggregate size. Close spacing of reinforcement may require a maximum aggregate size of less than 19mm.
- Workability
- Method of placement; and
- Any additional properties or performance requirements required for Special Concrete.
Normal Concrete
Normal Concrete represents around 80% of concrete production and is used when the designers primary concern is specifying the compressive strength of concrete (by 28-day strength within a range from 17.5 to 50 MPa). The concrete producer assumes responsibility for mix designs and their properties as defined in NZS 3104.
Special Concrete
Special Concrete refers to concrete where properties or performance requirements other than compressive strength within the Normal Concrete range (17.5 to 50 MPa) form the basis of the specification. For example:
- Concrete mixes over 50 MPa, or
- Where high early concrete strength is required, or
- Where characteristic other than compressive strength forms the basis of the specification (e.g. shrinkage, tensile strength, chloride durability etc.), or
- Where specific quantities of air entrainment are required.
The designer (or purchaser) is responsible for specifying the properties or performance requirements as well as testing and compliance tolerances of special concrete. The concrete producer is responsible for mix designs to meet these specified requirements.
Discussion with the plant engineer (nominated by the concrete producer) may be required when specifying higher strengths as factors such as aggregate strength and shape can be an issue.
Prescribed Mix Concrete
Prescribed Mix Concrete is limited to 10, 15, 17.5, 20, and 25 MPa nominal strengths at 28 days. Typical uses of prescribed concrete would be on small remote projects outside the operating areas of ready mixed concrete plants and therefore requiring site-mixed concrete production. Compliance is demonstrated by confirmation that specified mix portions (volume) detailed in NZS 3104 table 3 have been meet.
Firth Certified Concrete®
Firth Certified Concrete® is a Ready-Mixed Concrete with embodied carbon (EC) rating representing a percentage reduction of Global Warming Potential relative to the Infrastructure Sustainability Council of Australasia Baseline. The higher the percentage rating the lower the Carbon footprint for any strength grade (17.5, 20, 25, 30, 35, 40, 45 & 50 MPa).
| EC10 |
10% reduction -Typically available at all Firth Plants* |
| EC20 |
20% reduction - Typically available at all Firth Plants* |
| EC30 |
30% reduction - Available at selected plants, check with Firth |
| EC40 |
40% reduction - Available at selected plants, check with Firth |
| EC50 |
50% reduction - Limited availability, check with Firth |
* Check with Firth as some South Island plants may not have NZ manufactured cement available.
An Environmental Product Declaration (EPD) is a declaration of the past performance of common grades of Firth Certified Concrete® and is a standardised and verified way of quantifying the lifecycle environmental impacts of Firth Certified Concrete®. Firth's EPD is a "cradle-to-gate" type based on a consistent set of rules and is averaged over Firth's sites in New Zealand. It includes the environmental impacts associated with raw materials extraction and processing of inputs (cement, supplementary cementitious materials, aggregates, additives, and water), transport to, between and within the manufacturing site, and the manufacturing of the product up to the exit gate of the manufacturing site.
Firth can produce plant-specific and mix-specific environmental profiles on request, allowing consideration of three criteria (strength, cost & carbon performance). By contacting Firth Industries Limited through the Masterspec work section support function these services can be coordinated with the specification development process.
Preview the new Firth Sections
3101FC FIRTH LOW CARBON CONCRETE WORK – BASIC
3102FC FIRTH LOW CARBON CONCRETE WORK – STANDARD
3129FC FIRTH LOW CARBON CONCRETE PRODUCTION