Gradation, aggregate

The European standard CEN EN 12273 (2008) for slurry surfacing does not specify gradation limits. The target gradating and its tolerance range are left to be determined and declared by the producer/manufacturer. 

However, the American standard ASTM D 3910 (2011) and the guidelines of the ISSA (ISSA 105 and ISSA 143) specify gradation limits for slurry surfacing. The gradation limits specified per type of slurry surfacing mix, which are the same for both organisations, are shown in Table 6.4. 

Type 1 slurry surfacing is suitable to seal cracks, fill voids, repair moderate surface distresses (surface erosion) and provide protection. 

Type 2 slurry surfacing is suitable to fill surface voids, correct severe surface erosion conditions and provide a minimum wearing surface. 

Type 3 slurry surfacing is suitable to provide, in addition, maximum skid resistance and an improved wearing surface. This type of micro-surfacing is appropriate for heavily trafficked pavements and rut filling. 

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This combination yields a well-graded blend, and is similar to the aggregate gradation used locally in asphaltic concrete and used in the 1978 SWRI construction. The mix design yielded a binder content of 7.3 percent by weight as most satisfactory. 

Figure 1. Aggregate gradation for coarse aggregate materials...

The aggregate gradation that used in this experimental work is shown in in table 1. Table 1. Gradation of used aggregate... 

Aggregate Suitability Evaluation. As indicated earlier, most of the mixes studied were made with medium-coarse sand. However, a number of mixes were prepared to explore the range of aggregate gradations which may benefit from sulfur addition to asphalt compositions. The gradations in Table I cover materials from fine blow sands to coarse pit... 

Figure 7. Effect of sulfur content on Marshall stability for normal process mixes prepared using various aggregate gradations...

Cramer SM, Carpenter AJ (1999) Influence of total aggregate gradation on freeze-thaw durability and other performance measures of paving concrete. Transp Res Rec 1668 1... 

The influence of highway pavement surface type on tire/pavement noise was studied (Bennert et al., 2006). It was found that the open-graded friction course (OGFC) with the hot mix GRT-modified asphalts attained the lowest noise levels. Also, the GRT-modified OGFC mixes exhibited finer aggregate gradations than the traditionally used OGFC. 

The distribution of aggregate sizes is determined by sieving or sieve analysis. The aim of sieve analysis is to determine the aggregate gradation curve. 

Sieving procedure and aggregate gradation curve determination... 

The cumulative percentage with the corresponding sieve is plotted on graph paper and hence the aggregate gradation is obtained. The European specification suggests that both axes be linear, unlike the American specification that requires the x-axis to be logarithmic. 

Indicative aggregate gradation curves of the most commonly used asphalts are given in Figure 5.1. From the asphalts shown in Figure 5.1, the asphalt with most voids is the PA, whereas the asphalt with the least air voids is the MA. The rest of the mixtures in descending air void order are BBTM, AC (dense), SMA and HRA. 

The HRA, as well as the BBTM, is a gap-graded mixture. Their aggregate gradation lacks certain size aggregates for the given HRA mixture, the sizes from 2 to 10 mm are in small percentage, and for the BBTM, the sizes from 2 to 6.3 mm are also in small percentage. 

If the aggregate gradation passes beneath the boundaries of the aggregate restricted zone, consideration should be given... 

Eor the selection of binder, aggregate and possibly modifiers, see Section 5.4.2. Selection of aggregate gradation... 

Mix and compact the mixture with the selected aggregate gradation at five different bitumen contents (at the estimated content above, the estimated bitumen content 0.5% and the estimated bitumen content +1.0%). During compaction, keep densification data. Determine compaction and volumetric properties with respect to bitumen content. 

The aggregate gradation should fall within the limits given in Table 5.23. Tolerances of the produced mixture from the design (target) mixture are also given in the same table. 

If all requirements stated in Table 6.2 are fulfilled at binder contents above the maximum permissible, the mix design is repeated by altering the aggregate gradation and possibly changing the bituminous emulsion used. 

The determination of bitumen content and aggregate gradation is carried out with the same test methods as for hot asphalts after the water has been completely evaporated from the mixture. 

For the determination of the residual bitumen content and aggregate gradation, the representative samples are taken from the slurry machine, at the discharge point, according to CEN EN 12274-1. 

The determination of the aggregate gradation after extraction is carried out mechanically as per hot asphalts, according to CEN EN 933-1 (2012), ASTM C 136 (2006) or AASHTO T 27 (2011) and ASTM C 117 (2013) or AASHTO T 11 (2009). The tolerance ranges from the target gradation should be as those given in Table 6.4. 

The frequency of sampling for determination of residual bitumen content and aggregate gradation is recommended to be at least one every 5000 m. ... 

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