Ibrahim (1998) advised in his work that mixture composition and preparation of test specimens are significant factors affecting the behaviour of cold bituminous emulsion mixtures. So a number of measures were taken to ensure consistency in this laboratory work. For example, there are two approaches for preparing and using cold bituminous emulsion mixtures in the construction industry. These could be mixed and stored until they are needed or mixed and immediately laid. The approach used here was the latter as both time and space for storage were major constraints in this work.
For the laboratory compaction of such mixtures, there were two alternatives available as of the time that this research work commenced - the roller compactor, and the gyratory compactor. The gyratory compactor was opted for since it was capable of directly manufacturing the required cylindrical specimens without introducing any significant modifications to specimens.
The roller compactor produces compacted slabs from which the required cylindrical specimens would have to be cored out. Water jets are normally used as lubricant for the coring and there is the tendency for specimens to be significantly deformed during this process as a result of washing off of fine aggregates or flipping off of coarse aggregates. Cold bituminous emulsion mixtures at this desired stage are very fragile and so this method was not used at the mix design level.
Several methods have been advanced for curing as discussed in Chapter 3 of this thesis. In this exercise, no cyclic curing was done also due to the shortness of
144 time and considering the number of material types (5) that was investigated. The curing regimes did not involve the alteration of temperature nor relative humidity in the course of curing. The specimens were also only sealed while in the mould and unsealed when in the oven. The other factors considered during the laboratory manufacture of specimens are detailed in the succeeding sections.
5.9.1 Mixing
Two types of mixers - Hobart and Sun & Planet were experimented with in this laboratory work. The Hobart mixer was not used beyond the mix design stage because it frequently broke down. This was principally due to the fact that the available 20 Quarts Hobart Mixer was not designed for mixing the gradation (20mm DBM) adopted in this work. The coarse portion of the mix was frequently snagged between the agitator (flat type) and the mixing bowl thus preventing smooth movement of the agitator.
The Sun and Planet mixer effectively worked well during the mixing operation without breaking down. It also had the advantage that mixing temperature could be controlled in it. This eventually proved useful as it afforded the opportunity to investigate the effect of mixing and compacting CBEMs at two different temperatures on stiffness and other engineering properties of cured CBEM cores.
The results are later reported in this chapter. Figures 5.10 and 5.11 show the Hobart, and the Sun and Planet Mixers that were used in this work respectively.
5.9.2 Compaction
The Cooper Research Gyratory Compactor available in the NTEC laboratory was used for the compaction of the CBEM materials. This facility served a dual purpose in this work. These were in determining the compactability (compaction characteristics) of mixtures, and manufacture of cores for subsequent tests. In whatever capacity, degree of compaction is required to be close to what obtains in the pavement. Meanwhile, this compactor was found suitable as it was easy to operate and more importantly, density and shear stress values could be read off immediately as the machine compacted. The 100mm steel mould was used for the exercise in order to conserve materials. Although some other parameters were experimented with, as presented later in this chapter, a pressure of 600kPa, 50 gyrations, 30 rev/min and an angle of gyration of 1.25 which have been widely used by researchers (Jenkins, 2000; and Sunarjono, 2008 among others) were employed on the gyratory compactor at the mix design stage. Figure 5.12 shows the gyratory compactor. Since temperature could not be controlled in the compactor, each specimen (already in mould) was first placed in the conditioning
145 Figure 5.10: 20 Quarts Hobart Mixer
Figure 5.11: The Sun and Planet Mixer
146 Figure 5.12: Cooper Research Gyratory Compactor
147 chamber at the desired temperature for about 30mins before compaction.
5.9.3 Curing Method
As discussed in Chapter 3 of this thesis, curing is mandatory for studies on cold mixtures in order to obtain any useful information regarding their mechanical performance. Three curing regimes were eventually used in this work. For this design stage, an intermediate curing condition of 40 C over 72hrs was used. The curing was done using a forced draft oven. Early life and fully cured conditions of 40 C over 12hrs and 60 C over 96hrs were also later applied on specimens at the full investigation stage. The relative humidity was approximately 40% throughout.
The protocol followed was such that the specimens were left in the mould (in a sealed condition) immediately after compaction for up to 24hrs after which they were extruded. Specimens were subsequently placed in the forced draft oven at the required temperature for the specified time. Just before and immediately after curing, the specimens‟ masses were measured. The volumetric properties were measured after curing and then they were placed in the cold store at 5 C until they were ready for testing.
5.10 Compaction Characteristics and the Determination of OMC and MDD