or permanent slope protection along the sea shore 



Mattresses 



Along the lower part of the Mississippi where the strong 

 current undermines the banks along the bends, mattresses of as- 

 phalt mortar have been used extensively as a bank protection since 

 1932 c 



In April 1934- a great floating asphalt plant was put into 

 use for this purpose „ With this plant mattresses could be made 

 6.5 m in width and 190 m in length, reaching down to 50 m below 

 low watsr and covering slopes of 1^3 to Is 5. The maximum current 

 velocity was 2„4- m/see. 



In one season 7500 n? of asphalt mattresses, 5 cm thick were 

 placed „ The composition of the asphalt mortar was 12$ asphaltic 

 bitumen 30 /40, 22$ filler (loess) and 66$ river sand. The 

 mattresses were reinforced with steel wire netting (5 x 10 cm) 

 and provided with steel wire ropes , spaced at 0»9 m, for lower- 

 ing them into place <, 



In 1935 and 1936, reinforced asphalt slabls of 7 x 16.5 m 

 were used on the beach groins near Galveston and Florida City. 

 These slabs were placed under water with the aid of floating 

 crane s c 



This method was also used on mattresses of asphalt mortar, 

 size 13 x 5 m and 0»15 m thick, weighing 20 tons, which were used 

 on the outer slope of the North harbour dam at Harlingen (Figures 

 13, 14-s and 15). These asphalt slabs contained 20$ asphaltic 

 bitumen and 80$ sea sand, and were reinforced with four steel 

 wires of 1" diameter a Some slabs cracked while they were being 

 lifted, probably due to insufficient stretching of the wires 

 before and during the fabrication (Figure 16), 



Other mattresses of asphalt mortar, 15 x 5 m and o 05 m 

 thick were placed nearby These were fabricated at Harlingen 

 and wrapped around a drum 2 m in diameter after which they were 

 transported and put into place (Figure 17) „ Both types of 

 mattresses, which emerge during low water, have fitted themselves 

 perfectly to the uneven base and show few if any defects. 



Three slabs wrapped around drums were placed on the dumped 

 stone in front of the north east polder dike. The upper 

 part of these slabs has been destroyed completely | they contained 

 only 15$ asphaltic bitumen and proved to be very porous, probably 

 as a result of insufficient stirring of the mixture during trans- 

 portation from the point to the construction site. 



In preparation for the proposed drainage' of the Yssel lake 

 several asphalt mortar slabs 2 x 2 m, 0.06 m thick, and of varying 

 composition and reinforcement, were fabricated in 194.80 The best 

 result was obtained with a mixture of 15$ asphaltic bitumen, 15$ 



46 



