Unbound aggregates

Sayle et al. then considered the role of clustering in stabilizing defects in the bulk and at the surfaces of the material. The strength of the interactions between the components of a defect cluster is measured by its binding energy, in this case between an oxygen vacancy and two (7e + substitutionals. Clusters in the bulk and at the (111) surface are found to be bound whereas those at the (110) and (310) surfaces are unbound aggregation is not therefore expected on the latter surfaces. Simulations of Conesa also show a tendency towards defect association at the (111)... 

Hydraulic bound and unbound aggregates for road layer construction... 

Coarse coal refuse has been successfully used for the construction of highway embankments in both the United States and Great Britain. Coarse coal refuse has also been blended with fly ash and used in a number of stabilized road base installations. Burnt coarse refuse has also been used as an unbound aggregate for shoulders and secondary roads. Fine coal refuse has been recovered for reuse as fuel and is being burned in many cogeneration facilities now operating in the United States... 

Assesses susceptibility of compacted soil to frost heave Physical and chemical tests for aiding the selection and assessing the suitability of materials to act as bound and unbound aggregates... 

Figure 1.12 Cross section of springbox. (From Edwards J.P. et ai., Deveiopment of a simpiifled test for unbound aggregates and weak hydrauiicaiiy bound materiais utiiizing the NAT. Proceedings of the 6th International Symposium on Pavements Unbound, A.R. Dawson [ed.], pp. 3-i i. Rotterdam, The Netheriands A. A. Baikema, 2004.)...

Fleming RR., M.W. Frost, and C.D.F. Rogers. 2000. A comparison of devices for measuring stiffness in situ. Proceedings of the Fifth International Symposium on Unbound Aggregates in Roads, UNBAR 5, pp. 193-200. Nottingham, UK. 

Determination of the filler portion is important as its presence or absence in the mixture directly affects the behaviour of either the bituminous mixture or the unbound aggregate mixture. In general, too much filler is more harmful than the lack of it. However, the latter is unusual. 

The base course consisted of a number of layers whose materials can be unbound aggregates or hydraulically bound aggregates. 

The materials for the base and sub-base course are unbound aggregate mixtures or hydraulically bound aggregate mixtures. The aggregates may be crushed granular materials, manufactured materials from rock deposits or industrial by-products (slags) or recycled materials. The hydraulic binders, in the case of bound materials, are cement, fly ash, slag, lime, a mixture of some of them or factory-blended hydraulic binders for road use. 

Requirements of unbound aggregate mixtures according to European specifications... 

Table 13.1 Unbound aggregate base and sub-base quality requirements...

The formulae relating CBR and R value to subgrade resilient modulus do not apply to unbound aggregate base and sub-base. 

For the determination of the thickness of the pavement consisting of cold asphalt, there are two alternatives. One is for all the layers to be constructed with cold asphalts, and the other is for the cold asphalt to be laid over an unbound aggregate layer. 

Determine the thickness of the asphalt concrete layers over unbound aggregate base/ sub-base material, Tu, of 150 or 300 mm in thickness (use Figure 13.3 or a similar nomograph). 

Hence, the flexible pavement with cold base and unbound aggregate base/sub-base will consist of top 50 mm asphalt concrete, a layer of cold asphalt of thickness T A-base a base/ sub-base of thickness 150 or 300 mm, as selected. 

HBMs may be used as a replacement part of the total base/sub-base thickness and are always placed over an unbound aggregate layer. However, in case of using HBM, the methodology does not cater to any expected reduction of the overlaying asphalt layers. Details on HBM are given in Sections 10.5.7, 10.5.8 and 10.5.9. 

The design criteria used are as follows the horizontal tensile strain at the bottom of the asphalt layer or of the HBMs and the vertical compressive strain at the top of the layer no consideration was given for the unbound aggregate layer. 

The use of HBM eliminates pumping of fines most certainly to appear in jointed concrete pavements after a period of time, if unbound aggregate material had been used and joint maintenance is delayed. Pumping causes edge or corner cracking at the joints. 

The temperature adjustment factor for a three-layered asphalt concrete pavement (asphalt, unbound aggregate layer and subgrade) and for a full-depth pavement can be determined from Figure 16.41. 

---