The maximum thickness of a single compacted layer base can be up to 250 mm upon approval of the Engineer. The thickness of single compacted Wet Mixed Macadam (WMM) Base shall not be less than 75 mm. The base course material, according to ACI 302, 'Concrete Floor and Slab Construction,' should be 'compactible, easy to trim, granular fill that will remain stable and support construction traffic. It shall be laid on one or more layers as per line and level, grade and cross-section shown in the drawing or as directed by the Engineer. The entire subbase and base system should be at least 4 inches thickthicker if the engineer feels it is needed for proper support. The material is well mixed with water and rolled to a dense mass. Wet Mix Macadam consists of laying spreading and compacting of clean, crushed, well-graded granular materials on a prepared and approved Granular sub-Base. The material shall be free from organic or other deleterious constituents. The material to be used for the work shall be natural sand, crushed gravel, crushed stone, crushed slag, or a combination thereof depending upon the grading required use of material like brick metal, kankar and crushed concrete shall be permitted in the lower sub-base. SUB BASE (GSB) – it is being laid in road work because it plays two major rolesĢ- it provides a good sub-base to laid base layer on it. Components are mixed in mixing plant before spreading of mix, making the laying operation simpler & faster (A paver being used for the laying operation also helps).WMM uses more closely graded material, hence more stable.Although the spread method may be specified in the special provisions, CTB may be spread by one of three allowable methods: Type 1, Type 2, or Type 3. Hydraulic cement sets and hardens in the presence of water and remains durable and tough after hardening. Cement can be categorized into two main types depending on how it reacts with water. A paver (to spread the WMM mix) & a heavier roller (to compact the WMM mix). CTB specified as either Class A or Class B is generally used with asphalt pavements and can be either plant-mixed or road-mixed. Cement is made out of pulverized and crush stones mixed with chemicals such as lime and calcium silicate. Rolling is done using roller having min static wt 100KN.Mix is spread by a self-propelled paver finisher & in case of multilayer constn bottom layer may be spread using motor graders.Accounting for transit/evaporation losses. Material having CBR > 30% & PI 100mm & Grading 2 for layer thkness GSB material typically contain crushed stone > 50%.GSB material is a mix of sand & gravels, crushed stone & broken rock. ![]() GSB providing resistance against rutting.Common uses: Under roads or paths (where the. GSB reducing to stresses applied on subgrade layer. Stabilizing with cement improves the performance and longevity of the roadbase as well as its ability to compact.GSB act as a load bearing & strengthing component of pavement.Agg are used below base coarse & above subgrade layer is known subbase layer, due to granular crushed agg its called granular subbase.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |