The use of lime-treated British clays in pavement construction. Part 2: The effect of mellowing on the stabilization process

Abstract

The USA field experiences in the 1960s with lime treatment of marginal materials for pavement layers resulted in the introduction of a ‘mellowing’ period of between 24 and 72 hours, after mixing and prior to final compaction. This period facilitates reaction between the soil and the lime so that pulverization criteria and compact-ability can be achieved. As a result of these early experiences, the ‘mellowing’ period has become an integral part of specifications for lime-treatment processes used globally but it has been based on limited scientific justification. Under the Department of Transport (DoT) Specification for Highway Works (1991 and 1993 amendments) a ‘mellowing’ period of between 24 and 72 hours is mandatory. This period of mellowing is also recommended in volume 4 of the Design Manual for Roads and Bridges HA/74/95. 1 Part 1 of this paper, 2 also presented in Transport, discussed results of a research programme that investigated the effect of mellowing on the modification process of four British soils (Mercia Mudstone, Oxford Clay, Lower Lias and London Clay) treated with quicklime. This second paper presents the findings of the second phase of this research, which investigated the effect of mellowing on the stabilization process of the same four soils discussed in Part 1. Both papers suggest a need to improve the design methods for lime treatment of clays in the international procedures. 3

Lime stabilisation for earthworks: a UK perspective

“…Instead a weak and friable specimen, prone to breaking up, was produced (Sweeney et al, 1988). Other authors have similarly noted that increased mellowing periods promote a substantial increase in the percentage of air voids (Bell, 1988;Holt et al, 2000). The early lime-clay reactions introduce a brittle response and moisture conditioning to the wet of OMC will have only limited effects.…”

“…However, as sulfur swell issues from soil stabilisation are relatively rare and material from these potentially sulfur-bearing formations (see Figure 7 later) have also been successfully treated, it becomes apparent that the issue is more complex than this general association and Section 4.3 expands considerably on this point. Notwithstanding, industry experience suggests that sulfate swell potential is of specific concern with high sulfur clay soils that are also of high plasticity, with the Lias clay formation having notoriety in this regard (Holt et al, 2000;Snedker, 1996).…”

Family of Compaction Curves for Chemically Modified Soils

“…These results indicate that it is advisable to compact a stabilized subgrade without any delay. Holt and Freer-Hewish (2000) found insignificant reductions in pH of a lime modified soil after two days of mellowing. They suggested that this reduction in pH proves the completion of modification reactions.…”

Behavior of a Lime-Treated Expansive Soil

“…In fact, some researchers have shown that lime treatment may reduce the swelling potential of expansive soils (Holt et al, 2000;Al-Rawas et al, 2005;Panjaitan, 2014, Schanz & Elsawy, 2015, Nalbantoglu & Tuncer, 2001). For instance, Schanz & Elsawy (2015) concluded that the swelling potential, i.e.…”

“…Holt et al (2000) studied the effect of mellowing periods on the modification process of four British soils treated with quicklime and found that a half day mellowing period decreased the volume change (volume calculated by measuring of height and diameter of specimens subjected to soaking), but mellowing periods above half a day produced progressive increase in volume change, so that generally after a one day mellowing period the volume change was greater than that without mellowing (Figure 2.26).…”