Structural Concrete: Modelling
Description of methods and sub-methods for modeling structural concrete works in Baevr
TYPES OF STRUCTURAL CONCRETE OPERATIONS
Depending on the type of equipment and manpower required, structural concrete operations are classified into the following:
Structural Concrete – Discharge: This case comprises only of concrete production where concrete is simply tipped into the point of discharge without any vibration, compaction or levelling. Tipping may be off transit mixer from remote plant or manual wheelbarrows from site-mixer. Piling concrete is a simple example. It is assumed that the supply of concrete is immediately next to the point of discharge (no lead). There is no manpower associated with levelling and compaction as well.
Structural Concrete – Discharge & Vibration: This case comprises of concrete production and vibratory compaction as for example in columns, footings, walls and other cases where concrete is poured with shuttering on all sides. Concrete is considered to be directly tipped or carried in barrows over negligible distances. Leads and lifts, is any shall be separately modelled. No manpower is associated with levelling. Immersion type vibrators are to be considered.
General Structural Concrete: This case represents the generic case of concreting. It comprises of concrete production, leveling and vibratory compaction as for example in suspended slabs, tapered surfaces. Manpower required for levelling is quantified in terms of volumetric throughput of concrete.
Screed Concrete: This case comprises of concrete production and a screeding scenario (see different screeding scenario below). Screeding may be associated with additional vacuum dewatering and/or power troweling. Surface hardeners may be additionally added to the design or nominal mix.
Other cases of concreting not mentioned here include shotcrete, roller compacted concrete, mass concrete, micro-concrete etc. Leading or lifting scenarios, if any shall be accounted separately as a work apart from concrete composition.
CONCRETE PRODUCTION PROCEDURES
Remote-Batched Transit-Mixed: Components of remote-batched transit-mixed concrete as follows:
- Concrete Grade Designation, which is interchangeable as a material
- Homogeneous Batching Plant supported by loader and transit-mixer on stand-by
- Non-homogeneous transit mixer during hauling, which is to be neglected if the batching plant is located in site.
- Transit mixer on support during placement (or during placement + production)
Site-Batched Design-Mix: Components of Site-Batched Design-Mix concrete as follows:
- Concrete Mix Design
- Site Batching combined with one of the mixing scenarios
Volumetric Nominal Mix: Components of Volumetric Nominal Mix concrete as follows:
- Concrete Mix Design
- Mixing Scenario
SUPPORTING PROCEDURES IN CONCRETE PRODUCTION
Concrete Mix: Collection of procedures catering to different geographical locations and type of materials
Mixing Scenarios: Different mixing scenarios enumerated as follows
- Mixer: Mixer and manpower for loading are scalable
- Mixer + Loader: Mixer, loader for aggregates and manpower for cement loading are homogeneous. This scenario is used when number of mixer machines can be increased to optimize the utilization of loader.
- Mixer + Loader-on-Support: This is the most common loader-mixer operation. Mixer and manpower for cement loading in homogeneous combination. Loader remains on support to the working time of mixer.
Screed Vibrator: In this conventional method, concrete grade slab is levelled on grade with a screed vibrator that runs on prefixed rail channels. The rail channels are fixed on the grade after placing the reinforcements, such that concrete can be poured in alternate bays at a time. The channels act as the guage that controls the thickness of concrete. The screed vibrator compacts the concrete and is subsequently followed by removal of excess water using vacuum dewatering. The floor surface is then polished to requisite surface finish using a power trowel, with required finishing tools. The remaining alternate bays are poured in the next session, leaving a construction joint with the previously laid alternate bays.
Laser-controlled screeding machine: Laser controlled screeding machine does not require channels rails or guages. The machine is capable of controlling the level of concrete grade slab to reasonable thickness using laser beams. Screeding is followed by vacuum dewatering and power trowel based on the requirement of the project. Vacuum dewatering is now being progressively replaced by use of surface hardening additives.
Lifting & Leading scenarios
When concrete is associated with a lift (more likely than not) or lead, in addition to its haulage from batching plant to site, the same shall be considered as a separate scalable or stand-by work. Following different scenarios can be identified:
- Manual lifting by relay transfer: The total distance of lead/lift is used to determine the number of unskilled helpers required for a relay transfer. The speed of transfer is weight-of-parcel / interval-between-parcels. Any scaffolds or access ladders required for transfer shall be on direct mobilization.
- Concrete Pumping: Concrete pumping is achieved either using a line pump or boom pump. The pump is scalable to the quantity of concrete, whereas tremie pipes needed for conveyance shall be on special-purpose mobilization, to be quantified during take-off. Note that capacity of pump may be affected by the height of lift, which is addressed while selection of pump at specification-time. Boom length is limiting substitute.
- Hoist/Tower Crane: Ignoring the time of operation of hoist/crane (by loading large barrows in hoists/cranes) manpower may be required to move material to and from hoist/crane, which may be addressed using a leading scenario.