of 194-9. It is proposed to finish this work in 1950. The asphalt 

 mortar contained 20$ asphaltic bitumen 6o/?0, 10$ filler and 70% 

 dune sand. Before the pouring of the mortar, the top surfaces of 

 the stones were wetted to prevent the asphalt from sticking to 

 surfaces from which it would be removed by wave action after sg:- l * 

 time in any event . ' 



The following quantities cf pouring asphalt were used 

 successively* between the basalt set stones and in the road on 

 the North pier 250 kg/ra 2 ; between the heavy set stones (100-500 

 kg) 900 kg/m 2 j in the dumped stone (500-3000 kg) around the head 

 of the pier 1000-1500 kg/m 2 . The greatest care was taken to 

 fill the voids completely in order to avoid cavities in which 

 air and water pressure might develop. The new construction with- 

 stood the gale of 1 March 1949 excellently. 



In order to test the resistance of bituminous sand against 

 wave action, part of the dumped stone of a mattress which was 

 situated in the breaker z-one north of the North pier, was re- 

 placed by bituminous sand consisting of 2% asphaltic bitumen 

 60/70 and 95/2 dune sand. In total 225 m? of the mixture was 

 dumped on the mattress. 



It was learned from periodic soundings during more than a 

 y=ar, that ths bituminous sand is gradually disintegrated by 

 the.jwave action. Furthermore a great number of the American 

 stone borer (Petri cola pholadiformis) was found in s sample. 



In cooperation with the Rijkswegenbouwiaboratorium a con- 

 tainer with samples of bituminous sand of various composition 

 has been placed in the breaker zone so that it may be determined 

 which asphalt content is required to make the material proof 

 against the stone borer. 



f . Miscellaneous asphalt works on beach groins and harbour- 

 jetties. - In 194S the dumped stone deposits around the outer 

 sections of the Seheveningen harbour jetties were filled with 

 pouring asphalt. In the same year a beach groin built as a 

 sand mound covered with bituminous sand, was constructed in the 

 1944- gap in the Westkapel sea dike (Figure 2). In 194.9 the 

 reinforcement of dumped stone deposits of certain beach groins 

 of itelfland, and the province of North Holland (south of 

 Kamperduin and along the North sea shore of Ylieland will be 

 carried out. 



Conclusion 



In hydraulic works as in road construction, synthetic 

 asphalt has rapidly become a useful building material. Thanks 

 to the extensive research work of various laboratories, it is 

 now possible to produce asphalt mixtures with properties to 



63 



