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Abstract
The study to improve engineering properties of cinder blended materials was conducted in Mbeya region Tanzania. The low volume roads (LVRs) comprises of 75% of the whole road network and serves about 80% of population in Tanzania. The abundant materials in Mbeya region are cinders/scoria, pumices and volcanic soils which are originated from volcanic action. The samples from four source materials which are Ituha cinder, Ituha pozzolan, Mlimanyoka clay and Mbalizi gravel were collected for laboratory tests. Characterizations of source materials were conducted and grading coefficients (GC) and shrinkage products (SP) which are the requirements for selection of materials for surface layers of LVRs were computed. The results for GC and SP for all four source materials are out of range of 16 to 34 units and 100 to 365 units respectively. The California bearing ratios (CBR) at 95%MDD (maximum dry density) for four source materials are 17.6% for Ituha cinder, 25% for Ituha pozzolan, 3.2% for Mlimanyoka clay and 5.1% for Mbalizi gravel. The results for GC, SP and CBR for all four source materials indicated that the materials are not suitable for construction of surface layers of LVRs. The four source materials were blended together to get six blended sample materials targeting GC and SP ranges. The results of CBR values at 95%MDD for the six blended samples are 28% for 10MNCl40ITPo50ITCi0MBGr, 43% for 11MNCl40ITPo39ITCi10MBGr, 56% for 12MNCl35ITPo40ITCi13MBGr, 44% for 13MNCl32ITPo35ITCi20MBG, 39% for 14MNCl42ITPo44ITCi0MBGr and 53% for 15MNCl25ITPo35ITCi25MBGr. The improvement of CBR values of the six blended sample is because of enhanced interlocking and friction properties of the mixtures and addition of clay which act as binder to the coarse grain particles. It is important to develop suitable envelopes for surfacing layer materials of LVRs since interlocking and friction resistance are enhanced by gradation characteristics of material grain particles. For easy blending process of materials, an equation have been developed which can be used to blend materials using GC and SP parameters.
Highlights
Low volume roads (LVRs) are the roads which are designed and constructed to serve 50 – 300 vehicles a day with pavement layers and materials capable to resist vehicle axle loads up to 1.0 mil CESAL during its design life [1, 3]
The analysis of laboratory tested sample materials were based mainly on the parameters required for selection of materials to be used for construction of surfacing layers of unbound low volume roads (LVRs) which are shrinkage products (SP), grading coefficient (GC) and California bearing ratios (CBR)
The results indicates that Ituha cinder and Ituha pozzolan are non-plastic materials which are not suitable as surfacing materials for LVRs [1, 15]
Summary
Low volume roads (LVRs) are the roads which are designed and constructed to serve 50 – 300 vehicles a day with pavement layers and materials capable to resist vehicle axle loads up to 1.0 mil CESAL (cumulative equivalent standard axle loads) during its design life [1, 3]. The deposit materials available in Mbeya region are volcanic materials which are cinder/scoria gravels, volcanic soils and pumices [8, 11]. These materials have been categorized as marginal materials because they lack some engineering properties to be used for road construction [14]. They have high void contents which absorbs high amount of water, low specific gravity, relatively soft grains and have no binding properties [2, 4] These shortfalls have resulted into a low or improper usage of volcanic materials in Tanzania
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