VicRoads
SECTION521CONSTRUCTION OF ROLLER COMPACTED CONCRETE BASE COURSES
##This section cross-references Sections 173, 408 and 520.
If any of the above sections are relevant, they should be included in the specification.
If any of the above sections are not included in the specification, all references to those sections should be struck out, ensuring that the remaining text is still coherent:
521.01DESCRIPTION
This section covers the requirements for construction of roller compacted concrete base pavement courses.
521.02CONFORMITY WITH DRAWINGS
The concrete pavement shall be finished to a smooth and uniform surface and shall conform within the following limits to the levels, lines, grades, and cross sections shown on drawings:
(a)Level
The level of the top of each layer shall neither be less than the specified level nor exceed the specified level by more than 10mm, except against kerb and channel where the surface at the edge of the wearing course shall be flush with or not more than 5mm above the lip of the channel, unless otherwise specified or shown on drawings.
(b)Shape
No point on the finished surface shall lie more than 6mm below a 3m straight edge laid in any direction except across a crown.
(c)Alignment
The edge of the base shall be within 50mm of the plan location.
(d)Width
The width of the base shall not be less than the design width and not greater than the design width by more than 50mm.
521.03CONCRETE PLACEMENT
(a)General
Unless otherwise specified, concrete shall be spread using a paver except for small areas where use of a paver is not practical in which case manual placement methods may be used.
Concrete shall not be placed when the shade temperature is below 5C or above 35C and the temperature of concrete when placed shall be not less than 10C nor more than30C. Concrete shall not be placed when rain is falling or when rain is expected within one hour of placing. The Contractor shall have available on site sufficient waterproof covers to protect concrete laid within 1hour of rain falling. Covers when required shall be installed in such a manner as to not disturb the surface.
Concrete shall be placed, compacted and finished within 60minutes of mixing except that when the shade temperature exceeds 30C the concrete shall be placed, compacted and finished within 45minutes of mixing.
(b)Debonding of Subbase
A size5mm bitumen emulsion seal shall be sprayed onto the subbase 48hours before the placement of concrete. The seal shall be applied in accordance with the requirements of Section408.
(c)Paving Rate
The paver shall be operated such that its forward speed shall not be stopped due to lack of concrete. Should a essentially continuous rate of paving not be maintained, paving shall cease until appropriate remedial action is taken.
521.04COMPACTION
Concrete shall be uniformly compacted immediately after placement using a procedure which produces a dense layer having a uniformly textured surface and a profile satisfying the requirements of Clauses521.02 and521.08.
521.05JOINTS
Joints shall be constructed as specified and shown on the drawings. Joints shall be straight and vertical and transverse joints shall be continuous from edge to edge of the pavement.
(a)Construction Joints
(i)General
Construction joints shall be considered to be fresh joints when concrete on either side of the joint has been mixed within a 60minute interval, or 45minute interval when the air temperature is over 30C, and provided the concrete does not show signs of setting. All other construction joints shall be considered to be cold construction joints.
Where set retarders are used the above times may be extended subject to review by the Superintendent.
Longitudinal joints shall be constructed parallel to the centreline of the pavement.
(ii)Fresh Construction Joints
Construction joints during a day's production shall be made as fresh joints.
For longitudinal joints, rolling shall not be carried out within 0.3m of the proposed longitudinal joint during the first paver run. This initially uncompacted section shall be compacted together with the adjoining paver run.
For transverse joints, rolling of the initial strip shall be stopped 0.5m from the proposed joint and this initially uncompacted section shall be compacted with the beginning of the succeeding run to form the joint.
Placement and compaction procedures shall be such that full depth compaction and the specified surface finish is achieved at the joint.
(iii)Cold Construction Joints
The work shall be organised to minimise the length of cold joints. A cold joint shall be formed when the adjoining concrete has been placed outside the time requirements specified in Clause521.03 or where the adjoining concrete shows signs of setting.
The edge of the previously placed concrete shall be cut back by sawing the concrete with a power concrete saw to at least onethird the slab depth but not exceeding onethird the slab depth plus 10mm to expose an even, clean, sound, vertical surface for the full thickness of the pavement, without disturbing the concrete that is to remain in place.
Cold joints shall have the same texture, fulldepth density, and smoothness as specified for other sections of pavement. The edge of the previously laid concrete shall be cut back at least 200mm from the top edge to expose a dense fully compacted edge. Trimming shall be carried out by cutting with power saw to a maximum depth of onethird the layer thickness and breaking off with hand tools without undercutting. The broken back surface shall be free from dust, sand, or other foreign material when the joint is formed. The face of a cold joint shall be covered with a cement slurry placed immediately in advance of paving and covered with concrete while the slurry is wet. Cement slurry shall consist of 3parts water to 4parts cement by volume.
Cold transverse construction joints shall be constructed normal to the centre line and shall not be formed within 3.0m of a planned contraction joint.
For cold longitudinal joints the screed of the paver shall overlap the previously placed paver run by 25mm to 50mm and shall be sufficiently high so that compaction will produce a smooth, dense joint. Any concrete placed by the paver on the edge of a previously placed paver run shall be pushed back by use of a rake to the edge of the paver run being placed. When the quantity of concrete on the edge of the previously placed paver run plus uncompacted material in the paver run being placed exceeds that required to produce a smooth, dense joint, the excess concrete shall be removed.
(b)Transverse Sawn Contraction Joints
(i)General
To prevent uncontrolled cracking in the base, sawn transverse contraction joints shall be constructed. Sawing shall commence as soon as the concrete has hardened sufficiently to permit cutting of the concrete without excessive tearing or ravelling regardless of time or weather conditions.
Unless otherwise specified or shown on the drawings, joints shall be cut on a skew to the centreline of the pavement from the right side of the pavement and cross in the direction of design traffic flow at a 1in6 skew. Joint spacing shall be 10.0m0.3m and the line of a sawn joint shall not deviate from a 3m straight edge by more than 20mm. The joints shall be constructed to the dimensions and details shown on the drawings initially formed as a sawn groove 3mm wide to a depth not less than onethird the slab depth but not exceeding onethird the slab depth plus 10mm. Joints shall be sawn in the sequence of concrete placement. Before sawing a joint, the base concrete shall be examined closely for cracks and the joints shall not be sawn within 1m of a crack.
Where a crack develops ahead of the saw, sawing shall stop for that joint.
(ii)Sealing of Sawn Joints
Immediately after sawing, the joint groove and the adjacent concrete surface shall be thoroughly cleaned of all sawing detritus a continuous PVC spline seal 5 1mm in diameter shall be installed in the sawcut. The top of the seal shall not be less than 5mm nor more than 7mm below the surface of the base. Within 10days of initial sawing the sawn joints shall be widened to not more than 7mm, and deepened to a depth necessary to install the permanent seal. The widened sawn joint shall not exhibit more than 3mm of edge ravelling at any point along the joint measured from the top surface. The permanent seal shall be installed immediately after the initial sawcut is widened and the joint thoroughly cleaned.
Permanent seals shall either be neoprene compression type or an insitu cast silicone complying with Section520.
The installation of neoprene compression seals shall not proceed when the shade temperature exceeds20C. The joint groove into which the seal is to be inserted shall be clean and dry immediately prior to the installation of the seal. The sides of the neoprene seal shall be coated with a clear or concrete coloured lubricantadhesive compound complying with ASTMD2835 ‘Specification for Lubricant for Installation of Preformed Compression Seals in Concrete Pavement’. The seal shall not be overstretched in order to fit into the groove and the maximum increase in length of the seal after installation shall be5%. Any seal exceeding 5% extension shall be removed and replaced. The seal shall be continuous between longitudinal joints and where a discontinuity occurs the seal shall be butt jointed. The top of the seal shall be between 3mm and 6mm below the surface of the pavement.
The sealing with silicone sealant shall only take place when the side walls of the joint are surface dry and clean. Immediately prior to introducing the silicone into the joint a continuous polyethylene closed cell backer rod shall be installed in the joint as shown on the drawings.
(c)Expansion Joints
Expansion joints are generally formed around structures and features which project through, into or against the pavement and at other locations as specified. Transverse expansion joints shall not be constructed within 1.5m of a sawn contraction joint. Where necessary the spacing and skew of the adjacent transverse contraction joint may be altered to ensure sufficient clearance is obtained.
Expansion joints shall be continuous across the full width of the base normal to the centreline and constructed in accordance with the drawings.
The joint gap shall be 20mm running vertically for the full depth of the slab.
The top of the sealant shall be between 3mm and 6mm below the surface of the pavement.
Details of the proposed sealant and the method of insertion shall be submitted to the Superintendent for approval at least 2weeks before the commencement of installation.
The Superintendent may require a trial joint installation up to 2m in length of any proposed sealant, to be carried out prior to accepting the proposed sealant and method of insertion.
(d)MultiLayer Construction
Where specified, the concrete shall be constructed in 2layers of equal depth placed on the same day. If the time requirements given in Clause521.03 are exceeded a cement slurry shall be spread immediately in front of the paver at a uniform rate of 2kg of cement slurry per square metre. Any wheel tracks made in the slurry shall be recovered with slurry. The slurry shall be covered with concrete while the slurry is wet. Cement slurry shall consist of 3parts water to 4parts cement by volume.
The surface layer shall be placed so that transverse and longitudinal construction joints coincide with construction joints in the bottom layer of the pavement.
521.06CURING
Curing shall commence immediately after compaction is completed by keeping all surfaces of the concrete continuously wet. After the initial 12hours of curing, the pavement shall be cured for a further 7days by the application of a pigmented chlorinated rubber applied at an application rate of 0.3l/m2 curing compound. The curing compound shall comply with the requirements of Section520.
Any water applied to the surface of the concrete that is in excess of the amount needed to keep the surface of the concrete continuously wet, shall be controlled so as not to cause ponding on the concrete surface or erosion of the adjacent formation.
Water shall be applied to the concrete surface in a manner which will not cause erosion of the surface.
521.07FINAL SURFACE TEXTURE
The surface texture of the completed pavement shall be uniform over the whole pavement area and shall be totally free of any surface tears, pattern cracking, segregation, pumped areas, aggregate drag marks, areas loosened by construction operations, or areas where fines have been washed away during the curing process.
521.08ASSESSMENT OF THICKNESS, COMPACTION AND STRENGTH
(a)General
The concrete shall be assessed in lots and all lots shall be tested. A lot shall consist of work constructed under essentially uniform conditions and is essentially homogeneous with regard to material and appearance. A lot shall normally consist of one day's work unless there has been a change in materials or mix proportions which could affect the uniformity of the lot, or there has been a substantial interruption to the construction process requiring a construction joint to be made. In such cases the work shall be split into more than one lot and each lot shall be assessed separately for compliance with the specification.
(b)Cylinder Specimens
(i)General
The Contractor shall sample, prepare, cure and compression test the cylinders cast on site in accordance withAS1012.
The concrete shall be sampled from the back of the paver. Each sample shall consist of one cylinder specimen for testing at age 28days.
Cylinder specimens shall be 100mm diameter by 200mm high and compacted using a vibratory hammer.
A lot shall consist of ten samples.
The Contractor shall adopt an unbiased sampling program for the day's production. If the casting process is unexpectedly interrupted or terminated the samples taken to that time shall represent the lot.
(ii)Density Testing
The saturated surface dry density of cylinder specimens (Cc) of a lot shall be determined in accordance with AS1012 Part12 at the same age at which the density of cores of the lot are determined. The mean cylinder density(Cc) of a lot shall be calculated using all the compressive test cylinder specimens in that lot.
(c)Cores
(i)General
Density testing shall be based on cores taken from the concrete pavement when it is 7days old. The bounds of each lot for density and thickness testing shall be selected to coincide with the lots selected for compressive strength testing and, within the lot, sites for testing shall be selected on an essentially random basis except that no site shall be selected within 150mm of a joint or slab edge. For each lot ten cores shall be taken.
Cored specimens taken for density testing shall not be used if they are damaged during the coring operation or during transport. Rejected specimens shall be replaced with other specimens from the same lot.
The Contractor shall restore core holes within 24hours of cores being taken. The quality of concrete used for core hole restoration shall be equivalent in strength to the surrounding base concrete.
The surface of the restored hole shall be similar to the surrounding concrete surface in texture and colour and shall be covered with a curing compound.
(ii)Density
The saturated surface dry density of cores shall be determined in accordance with AS1012 Part12 and the mean core density (Cf) of the lot determined using all density test values from the cored samples in that lot.
(d)Assessment of Compressive Strength
(i)Unadjusted Characteristic Strength (Du)
Where 8 or more test values of 28day compressive strength of a lot are available the characteristic strength of the lot shall be calculated to the nearest 0.1MPa in the following manner:
Du = x ks
Where:Du=unadjusted characteristic strength of the lot
x=average cylinder strength of all specimens from the lot
s=standard deviation of cylinder strength of all specimens from the lot
k=a factor which depends on the number of specimens in the lot as shown in Table521.081.
Table 521.081
n / 8 / 9 / 10k / 1.42 / 1.40 / 1.38
Where less than 8test values of 28day compressive strength of a lot are available the characteristic strength of the lot shall be calculated to the nearest 0.1MPa in the following manner:
Du = x 3
(ii)Adjusted Characteristic Strength (Da)
The unadjusted strength of the lot shall be adjusted for compaction in the following manner:
The mean field density of a lot (Cf) shall be calculated using all field density test values from the cored samples in that lot.
The mean density of the cylinder specimens of a lot (Cc) shall be calculated using all the compressive test cylinder specimens in that lot.
The density ratio of the lot (Rc) is defined by:
Rc = / 100 C fCc
The unadjusted characteristic strength of the lot Du shall be calculated as follows:
Da = Du [6.94 / Rc / - 5.94]100
If Da exceeds 35.0MPa the lot shall be accepted. Otherwise the lot shall be considered in accordance with the General Conditions of Contract subClauses30.3 andS8.1.
(e)Assessment of Thickness
The thickness of a lot shall be determined as follows:
Within the lots defined for assessment of compressive strength the surface levels of the subbase shall be measures as specified in Section173. Levels of the base surface shall be taken at the same locations as taken on the subbase. For each lot the measured differences(Xi) at each location shall be calculated to the nearest 1mm in the following manner:
Xi = (base level)i (subbase level)i
The departure of the lot thickness from the design thickness shall be calculated to the nearest 1mm in the following manner:
T = D x
Where:T=departure of the lot (mm)
x=mean thickness determined from the level differences(Xi) for the lot(mm)