Should roads designed in high rainfall areas be rigid pavements?
Should roads designed in high rainfall areas be rigid pavements? I ask this because in Eastern part of NIgeria, where it rains heavily, the roads are a menace, is it that the designers did not forsee this during the prediction or that there is a problem? What is it and how can it be corrected as these roads are all failed and spoilt roads,pot holes, and all forms of road failures exist
Despite the level of rainfall, the soil condition determines the kind of pavement to be constructed.The analysis of the soil conditions California Bearing Ratio(CBR), MDD – Maximum Dry Density. MWD(Plasticity Index, Liquid Limits and Plastic Limits) – Maximum Wet Density. OMC – Optimum moisture Content is the determimg factors.
Use of asphalt/bitumen is the best but drainage is paramount, failure to drain the water off the bitumen surface will lead to pot-holes, in Uganda where I reside this has been a major issue, water stagnant on the these asphalt surfaces (get the right cross gradient).
There is an old adage in road engineering which says that the three most important things to deal with are Drainage, Drainage and Drainage. No matter what type of road pavement is used, the design must include provisions for leading surface water off the road, dealing with water getting onto the road from the edges, and ensuring that water under the road can be drained away. The surface is not the primary factor, one must look at the whole picture and design the full roadway (shape, alignment., levels, foundations, cross drains,etc.), to deal with drainage. The choice of materials to use in both the road foundations and the structural layers is important as these have a big influence on costs.
Dear Alan, the adage that I've heard was "Compaction! Compaction! Compaction!!". I'm my opinion, once the design compaction is achieved, I would say that you'll get a long lasting pavement, as per design, but there are other factors, and drainage system design is one of them. In general, I agree with you when you say that you have to look at the whole picture and transversal slope plays a big role to achieve a correct drainage and affects not only the pavements life but also the riding safety.
What I don't believe is that using a rigid pavement in heavy rain fall areas would solve the problem. Just construct a good pavement (from foundation to wearing course) and a better drainage system that is adapted to those heavy rains!
I agree with you on the importance of compaction,which is is another factor affecting quality and performance. Good design, good materials. taken together with good quality construction and maintenance are the keys.
In my opinion, rigid pavement cast using RC or concrete is best option for an area with heavy rainfall and where it is not possible to provide proper drainage for surface run-off. It is suggested that these pavements must be designed based upon the actual value of the sub grade modulus in wet conditions for given traffic. Good compaction will results in some cost cutting.
Obviously rigid pavements are more durable but economy precludes their use as a first choice. Flexible pavements are equally durable under rainy conditions and examples abound in areas such as Malaysia, Indonesia, Philippines, and others places which experience more rainfall than Nigeria. Attention should be paid to specifications, material quality, workmanship and sub grade conditions. Above all timely maintenance will increase the life-span of your roads.
The road surface should be considered as asphalt pavement or concrete pavement, in both type, it is needed adequate layer contain sub base and base, but essential part of the road design is considering a suitable derange system based on hydrological and hydraulic study and design.
You don't have to forget that a road is at the end a civil structure and you should think about it as that. This means that foundations are very very important. If you are going to build a road on a place where heavy and steady rains are daily, first of all you should look at the place where you are building. A good soil mechanics study is compulsory to understand the capacity of load of natural terrain and then design the complete paving structure in accordance with the loads you are going to put on top of it and the transit intensity the pavement should face in it's life cycle.
A good work in the natural soil should be necessary to drain it. Then all the sub-grade and all the layers on top of it. Base, sub-base, or whatever the design requires. Drainage of the structure is, as has been said, key factor. The faster you get rid of water in the structure, the best. The pavement should have enough slope as to drain fast the raining water and good channels on both sides of the road to convey water to the art work to dispose of it.
Finally, the pavement. A good pavement should be capable of outstanding behavior under rainy conditions. Concrete pavements usually performs better under water than asphalt, but again, drainage and compaction of sub-base and foundations are also key factors.
Usually holes in the pavement are a mean some problem under them is developing, unless it is bad quality of concrete or concrete placement.
The problem with concrete pavement is that since it is rigid, any deformation under it, should develop additional stress in the paving slab, and if the slab is not prepared to resist such stresses, it will fail by cracking or braking, starting the complete process of deterioration not only of the pavement surface, but also the base and under structure, so the effect of water is exponential.
If it is a water-logged area, rigid pavement would be the best option. If it because of excessive rainfall and the place is not water-logged while not go for flexible pavement which is more economical. However, foundation of the road is very important which include the nature of soil for placement and adequate compaction. Also, serviceability appurtunances should be put in place, these include: adequate drainage system, weep-holes and sufficient camber.
If the asphalt has a high sulfur content, then it will be transformed into sulfuric acid causing a serious damage to the road under heavy rain falls. In this case certain additives should be added to the asphalt mix to prevent the oxidation process of sulfur in the asphalt.
After correlating the errors, the model fit appears just great (Model consists of 5 latent factors of the first order and 2 latent factors of the first order; n=168; number of items: around 23). However, I am concerned with how to justify the error terms correlations. In my case the wording of two items appear very similar: With other students in English language class I feel supported (item 1) and With other students in English language class I feel supported (item 2)(Likert scale from 1 to 7). According to Harrington (2008) it's enough to justify the correlation between errors.
However, I would appreciate any comments on whether justification of similar wording of questions seems enough for proving error correlations.
Any further real-life examples of wording the items/questions or articles on the same topic are also well-appreciated.
In this study the engineering characteristics of concrete mixtures containing dihydrate phosphogypsum, a by-product of the wet phosphoric acid industry, is investigated. Phosphogypsum-based concrete mixtures consolidated by impact compaction, external high-frequency vibration or static compaction are studied in unconfined compression, splitting ten...