Best practiceHand lay PQ concrete

Change Issue When ReasonMajor Update Dec 06 Major ReviewSpec clause at issue :09 Originator:kevin.robinson@amec.com

Associated best practice sheets1. Instructions for the operation of LLI rotary percussion drill mount.2. Daily PQC Checklist – P&IT Form 089

HistoryRoad forms with a rounded edge had been used originally these have now been superseded and only square edged forms should be used. More recently a new design of road form has been introduced and will eventually replace all the old style forms.Development of a higher strength concrete has reduced the workability of the concrete in hand lay work.

Safety, health and environment

1. Drilling operations for road pins for the old style forms should be carried out using the drill mount or alternative remote controlled drills to help prevent hand arm vibration.

2. The new road forms use ???? bolts for fixing 3. Only approved Triscreeds should be used. These have all moving parts protected

. See notes below about Triscreeds.

Planning the work

Hold advance-planning meeting at the outline design stage for development of the Target cost. The Planner, Paver Foreman, Senior Engineer/Agent, Material Engineer and Designer should attend. If possible the Estimator should attend, otherwise feedback outcome to him.The purpose of this is to: -

1. Decide the concrete supply strategy taking into account the travel time, transport and required / achievable outputs & batcher capacity.

2. Plan for regular daily out puts. 3. Review and agree the best lane layout and pour sequence, Pit/manhole,

joints and AGL positions. Note the design requirement for AGL positions to be a minimum of 500mm from any joint.

Pit locations within pavement

1. Pits/MH’s should be positioned with one edge on a transverse joint. Their position should be such as to allow for the concrete lorries to reverse between them and the forms. If this is not possible, this lane will need to be side tipped from a previous pour.

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2. One pit edge should also ideally be placed on the longitudinal joint, off-set sufficiently for an "E" joint to be formed; otherwise the pit off-set should be sized such as to provide a suitable infill slab.

Programming

1. Plan to set up your first bay towards the centre of the bay layout, this will maximise the use of the forms as you can stitch on to each side of the first bay (having allowed it to cure for 2 days).

2. Design a laying sequence, which minimises the transport of road forms. Road forms erection should reflect this and should proceed at least one day in advance of concreting.

3. In the winter, with a PFA mix, it may be necessary to allow 3 days curing. In this instance, use the “stitch on” method at two locations (i.e. two sets of forms) and alternate pours between them.

4. Failure to allow sufficient curing time will result in surface damage caused by the Tri-screed running on the not fully cured surface of a previously completed pour

5. If bays need to be trafficked for access then the required strength should be confirmed with the designer and the work programmed to accommodate. Note strength requirement will vary according to slab thickness.

6. Consider access routes for lorries/dump trucks, including reversing and turning. This may be dictated by the need to have access to back concrete lorries down the bays to be concreted. End tipping is slow and difficult over side forms.

7. For small pours with difficult access it may be better to deliver concrete in agitator to simplify placing.

8. Irregular bay shapes should be sized and sequenced such as to provide the most practical bay shape / saw cutting profile. Rules exist regarding aspect ratios and permitted included angles – refer to the Designers for acceptable parameters. Poorly designed bay shapes have a reduced life span and ultimately break up to form a F.O.D. hazard. Small / irregular bays take a disproportionate amount of construction time. Leaving too many of them until the end may unnecessarily prolong the construction programme.

9. Plan for regular daily out puts. 10. Consider the effect of the time of year and daylight hours on the daily out

puts.11. Check availability of road forms

Height of forms should be 25mm less than the PQ slab thickness to allow for slight variations in the surface of the WL/DL.

If new forms are to be purchased, allow 10–12 weeks for procurement If forms are from internal stock, check their condition and grit blast clean

as required. Pins for road forms should be 22mm diameter. Pointed (not guillotined),

cut to a length equal to PQ depth plus 100mm and driven to 25mm below the top of the road form. Purchase ALL pins – DO NOT HIRE

Stitch method

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Existing PQ

pans

Bay1

…………………………………………………………………………………………………..

bay5Possible stitch method after the initial pilot bay laid

…………………………………………………………………………………………………..

bay3

Bay4

………………………………………………………………………………………………

bay2

3. It is important that the lane vertical edges are smooth and bitumen coated to allow each lane to move independently of adjacent lanes with minimal restraint.

Consult: - Airside civil engineering reference Specification section 11 AndReference drawings: -

Drawing Nos.: -

BAAPITREF-C-016-2 to 027-2 inc. BAAPITREF-C-030-2 to 042-2 inc.

The drawings above represent laying of pavement in all possible situations. Check for a relevant drawing.

Method of work

Preparation

Ensure all deep services have been placed ahead of concrete operations.

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Existing PQ concrete

Existing PQ concrete

Pilot bay

During this process double check that all ducts beneath the PQ have been installed and correctly positioned for AGLs and that the ducts are clear.

Monitor the weather closely before committing to the day’s production. Obtain a suitable weather forecast. PQ can be laid within 4 hours of the probability of rain without covering. In winter, with PFA, this can be extended up to 8 hours (This is based on the provision that two coats of curing compound are applied 10 minutes after finishing). Plan on this basis rather than on the basis of covering the PQ to protect it. The ability to place PQ is also affected by low temperature, the presence of frost or very high temperatures. Wind can also have a significant early drying impact.

Set out pins and lines to the inside face of road forms. Check dips off the lines to ensure that the Wet Lean level is within the TARGET

range of +0 to -20. Aim for the higher end of the range for the Lean Mix level and the lower end for the PQ level. However, it must be remembered that the PQ slab thickness MUST NOT be less than that specified (-0 to +20)

Make good the lean mix if necessary to remove imperfections which would interfere with the movement of the pavement to be laid. Note: wet lean provides a more durable / better surface than dry lean but check areas where AGL ducts have been installed and areas that have been trafficked.

Fix road form to line and shim up to level using steel or plastic shims to suit the situation.

Pack gap beneath the forms both front and back with a sand/cement mixture that is strong enough to contain the concrete but weak enough to break out easily. 5 to1 for >20mm gap 12 to 1 for <20mm gap Forms should be packed 12 hours before use to allow packing to harden

Set stop end at start of lane. Bitumen spray the Lean Mix (rolling the drum well, to mix the bitumen, before

use). Check the Tri-screed before use and at regular intervals, to ensure it is straight

(”level”) when supported at the same centres as the Road Forms. Note re new triscreeds

Placing and finishing the concrete

The PQ daily check list (P&IT Form 089) should be completed prior to the start to the pour. This forms checks that all the right batching procedures are in place and checks carried out to deliver consistent compliant concrete. This form covers the target compaction factor, air entrainment and takes account of method of transport, delivery time etc.

Laboratory technicians may be required at both the batcher and site to correlate the C.F and air entrainment requirement at the batcher to ensure the specification is met at the point of deposition.

The banksman controls the tipping of concrete at the point of deposition. Remember to erect barriers and signs to keep out unauthorised personnel and direct deliveries.

Concrete delivered to site in a tipper wagon must be laid within 1 hour of batching; any load, which will fall outside if this window, should be rejected. This is a planning issue and should have been taken into consideration at planning meeting.

Concrete can be delivered in spinners; this would be a decision made at the original planning meeting. When delivered by this method the time between batching and deposition will be 2 hours.

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Batcher should be told required rate of supply (m3/hr) – site to keep batcher updated on the actual transport times being experienced (these can vary throughout the day). This can help prevent lorries queuing on site and hence concrete being held too long before placing.

The excavator spreads and compacts using the backactor mounted pokers leaving a small surcharge above the road-form. see notes below about use of backactor mounted pokers.

The winch men winch the Tri-Screed (This must be fixed firmly to pins or a Kelly block) over the concrete ensuring that all vibrators are working and that it is not pulled over low concrete, otherwise it will have to be taken back to repeat the process.

Time is lost in hot weather if the above is not controlled and this is particularly important, as the concrete ahead will become too hard to finish.

The shovel men skim forward any light surcharge in front of the Tri-screed and bank the backactor mounted pokers. They also use handpokers to complete compaction along the edges.

The excavator pulls forward any excess build up. 1 pole man uses 900mm easy float across transverse width to fill any open

texture and surface unevenness. 2 edge finishers float the outer 0.5m width each side. The edge finishers must only work the concrete the minimum required as over

work will result in the edge spalling. If excessive work is required look at the mix design or batching practice.

The brush man floats any central open texture and then applies two transverse brush strokes using a 900mm wide ????? brush. Note wider brushes make it difficult for the brushman to reach.

The brushman works off a Youngman platform sitting on the forms (see photographs) and is assisted in moving this forward by the edge men.

Spray with one coat of Aluminised curing compound (This should be carried out within 10 minutes of finishing or immediately the Tri screed and brushing operations allow access and the men are safely clear). In hot or windy weather the early application of compound becomes even more important as loss of moisture will result in surface cracking.

Apply a second coat of Aluminised curing agent within one hour of first coat to ensure full coverage. There should be a visual inspection that coverage is being achieved and corrective action taken if areas are a being missed. A further check on coverage can be made by measuring the volume of compound used. The coating applied must be evenly distributed, check at intervals that the coating is not pooling in areas.

Set out the joints and strike the forms as soon as concrete set allows. Saw cutting must be carried out after the very initial set of the concrete, but in

advance of the main curing shrinkage. Timing of crack cutting is critical in warm, dry, windy weather - less so in winter conditions. Monitor the concrete closely in warm weather and be prepared to saw from 6 to24 hours after placing. Timing must be judged by an experienced person.

If required you should consider an overnight 2-man team for sawing.

Use of backactor mounted poker sets

The backactor mounted pokers are a key item of equipment and must be correctly used to achieve adequate compaction of the concrete. Note: the excavator drivers are often inexperienced in placing concrete and have obscured vision from their cab of the pokers.

Brief driver on use of pokers

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A member(s) of the concrete gang, generally the shovel men will be appointed to direct operations and ensure the concrete is all fully compacted.

Prior to start of concretingo Check pokers are operating and correctly / securely fixed. They

should be spaced 300 to 450mm apart.o Pokers must be fitted to correct machine with sufficient power. ?????o Establish reference point on bucket so driver can tell that pokers are

being inserted to the correct depth.o Spray poker bucket with release agent to ease maintenance / cleaningo Check spare pokers are availableo Note: Pokers can be easily damaged by overcrowding the bucket

leading to snapping of the rubber mounting. Concreting

o The banksman will direct operationso Pokers generally should be inserted at a slight angle down from

horizontalo Pokers must be moved slowly through the concreteo The pokers must be moved in a systematic pattern to ensure all areas

of concrete are adequately compacted. o They must be left in the concrete long enough to remove all entrapped

airo The pokers must not touch the base or sides (forms)o Hand held pokers should be used to finish the edges

Triscreeds

Only approved triscreeds shall be used. These must be thoroughly cleaned immediately after use to avoid build up of concrete which will impair performance and properly maintained.The specification for the approved triscreeds has been developed from experience and incorporates our required safety features.

Multiquip ?????? with enclosed shaft. Petrol powered (arrangements need to be made for supply and storage of petrol).

Finishing PQ puts a lot of strain on the Triscreed. Externally hired triscreeds generally do not comply with our safety requirements, are not robust or reliable enough for working on PQ and have insufficient power to finish the concrete – in the past this has led to two triscreeds being used. Not only is this inefficient and non cost effective but it also extends the finishing process which can cause difficulty in achieving the required finish.

A backup Triscreed should be immediately available in case of breakdown.

Protection of the Finished Concrete

No tenting is required for curing (this is done by the curing compound) Covers are for protection of the green concrete from rain damage. There

should be risk and cost assessment to decide on whether covers are to be used.

In the event that paving will be undertaken during periods of cold weather, frost protection mats should be available to protect the freshly placed concrete from frost damage.

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When the ambient temperature is predicted to fall below 4 degrees centigrade, the freshly placed concrete shall be covered with frost protection mats as soon as possible after it has hardened.

The mats shall remain in place until such time that the concrete is no longer at risk or site cured cubes have reached 20mpa compressive strength.

Transport of concrete

It is important to determine the correct number of wagons to deliver concrete at the required rate.

Batcher should be told required rate of supply (m3/hr) – site to keep batcher updated on the actual transport times being experienced (these can vary throughout the day). This can help prevent lorries queuing on site and hence concrete being held too long before placing.

Monitor for gaps or standing wagons at both the paver and batcher. Review the cycle times for wagons as an ongoing exercise to ensure flow is

at the optimum and enable correct number of wagons to be ordered. Plan a rota for wagon driver refreshment breaks so that lorry availability is

constant. When calculating number of lorries allow for breaks and tachometer

restrictions. Transport lorries should be arranged to start work at the time concreting starts

not when the paver starts setting up. This avoids them standing during the mobilisation period.

Shopping list

Plant Placing Fixing PQC Roadforms

17T wheeled excavator with poker bucket 13” HF pokers for edges and inaccessible areas 2Tri-screed 1Curing agent sprayer 1Youngman boards 1Easy Float 1Concrete saw c/w water bowser & blades for cutting 1 “Green Concrete” (inc. spare). 3KVA Generator and Skill Saw (for stopends) 1

Hiab or other means of transporting forms as required 1Bitumen Sprayer 1Rock drill (Mounted) or Impact Wrenches 1depending on type of forms used Road Pin Extractor 1 Pin holder

Points to consider: - Regular maintenance must be carried out on the tri-screed to ensure no

deformation has occurred and all moving parts are functioning correctly. Paving foreman should ensure standard equipment is available such as

gloves, masks’ goggles, floats, brushes, shovels and easy float Check you have sufficient pans to meet programme requirements Ensure the required amount of R90AL spray compound is on hand and shelf

life has not expired.

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If the policy for the project is to use covers then a rubber duck plus labour will be required to move the covers.

Check the correct size covers and the c/w lifting beam are available, if covers are a requirement.

Availability of Frost blankets if appropriate time of year. Order pins for forms and setting out if none available. Or bolts for new PQ

pans.

MaterialsSteel shims, plastic shims, sand & cement for packing forms

Labour requirements (concreting)

PQ Supervisor 1Tri-screed operators 2Shovel operators (also bank poker buckets) 2Edge finishers 2Easy float operative 1Brush finish/curing spray operative 1Banksman 1

For large continuous pours then an additional skilled operative is required to cover breaks. It is also useful to have someone in the team qualified to drive the excavator.

Labour Requirements (forms)General operative 1 Carpenter 1Plus labour and plant for moving forms

Engineer 1Chainman 1

Outputs

5 to 6 m. wide bays For F6 mixes 400m2 / day @24m3/hr output + plus daily mob./demob. and movement.

Note: This figure needs to be justified through recorded data. A figure for F7 mixes needs to be determined.

Actual figures for the fixing and striking of forms, inc. resources employed, need to be determined

Batcher should be advised on required rate of supply

Items that can affect outputs

1. Bay sizes/lengths (and the consequent number of moves)2. Bay shapes

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3. Bay locations4. Variable weather5. Wet weather6. Concrete supply/batcher capacity7. Workability of concrete i.e. F6 or F7

In the worst cases these can reduce output by a factor of 5

The main limiting factor affecting output is the area to be finished in relation to the gang size. The Batcher / concrete transportation should be sized such as not to restrict the gang’s output however it is important not to overstretch the gang as this can lead to lack of compaction (insufficient time) and finishing problems.

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