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Construction Guide

Road Building With Ferrocement

What follows is from the experience of people living in a mountainous area. They have little money and need a good road during rain.

A roadbed of sand and gravel is best. A strong surface made of ferrocement keeps the road bed undamaged by use. A surface made of ferrocement is 3 - 5 centimeters.

The roadbed carries the weight of vehicles. There is no traffic weight limit for the ferrocement itself. Quality plaster used in ferrocement is four to six times the compression strength of concrete.

A very economical road is constructed with two 40 to 45 cm strips (16"). One strip for each side of the vehicle. Two layers of welded wire are offset to create a 38 cm wire grid (15"). The welded wire sits on two #3 bars, which are yellow in the graphic example below. The final width is 16 inches (41 cm) after plaster is applied. This width provides a 1/2 inch (1.25 cm) covering of the steel on each vertical side.

The rebar is set up off the ground on support blocks (2.5 - 3.75 cm) (1 - 1 1/2"). The total finished thickness with 3/8 - 1/2 inch (1+ cm) of plaster covering the steel on top is 2 1/4 - 2 3/4 inches (5.5 - 7 cm).

drawing of ferrocement road steel

If the ferrocement is used on native soil with soft or clay areas, then it should have more steel and be 6 - 10 centimeters thick (3.5 - 4"). This is true for a full width road as well as for the tire strip method of pavement. It is wise to remove some native soil and substitute sand and gravel where the soil is very soft. Good drainage design is also important. Ferrocement pavement will span small areas that are soft but it will break if the span is too much and the load is heavy.

A third layer of welded wire can also be placed under the bars. The cross wires should be aimed upward and the long wires down.

Small girders with extra steel can be carved into the road and cast into the pavement during construction. This might be desired where an artesian spring is in the road. Drainage comes first, then consider ideas about incorporating girders under the pavement.

Repair to a soft area that was not noticed during construction is accomplished by breaking the plaster with hammers, packing gravel, sand and the broken plaster under the exposed steel, and reapplying plaster. This is very rare because ferrocement pavement is so strong.

Ferrocement pavement is almost exactly the same as the floor for most ferrocement water tanks.

Placement of plaster can be from large trucks or mixed and placed entirely by hand. Large trucks can move forward on the steel and the support blocks can be put under the steel as work progresses.

One should double the thickness where ferrocement meets existing pavement. This is important mainly for providing the clearance for a smooth union. The traditional road will be repaired and resurfaced many times while the ferrocement road will be maintenance free for decades.

The most common mistake with ferrocement pavement is edges which taper to very thin and do not have steel. These thin edges can break and expose steel to weather. Make nice round edges and vertical sides to avoid this problem.

This pavement may not meet academic definition for ferrocement. However, roads constructed like this on poor soil have been witnessed to give good service for more than twenty years, with almost zero maintenance or degradation. Ferrocement is also identified by good service and long-life.

I have closely observed large trucks carrying 7.5 cubic meters of concrete pass by. The road was constructed exactly as the illustration above. I saw a soft area compress under the tires and then rebound with no damage, approximately 5cm = 2 inches of deflection. There were no evident damages.