475 kg/m^ of pouring asphalt, consisting of 13$ 

 asphaltic bitumen 50/60, 1% filler, 35$ dun© sand and 

 45$ "pearl" gravel was used. In 1947 other areas were 

 repaired by roughly setting the basalt stones on a thin 

 base of rubble stone and filling the spaces with pour- 

 ing asphalt, consisting of 11% asphaltic bitumen 50/60, 

 9% filler and 74$ dune sand. 250 kg per square mater 

 of pouring asphalt rare used, which filled the spaces 

 in the rubble stone base as well. About 12 kg/nr of 

 asphalt remained on the upper ends of the stones. This 

 was removed by wave action (Figures 5* 6, 7, and 8). 



The protection built in this way proved satis- 

 factory ', practically no damage was caused by gales. 

 The designers state that this construction method must 

 be considered as an experiment. Due to the urgency of 

 the work and the lack of time, there was no opportunity 

 to investigate the economy and efficiency of this con- 

 struction in comparison with others which might have been 

 preferable. In spite of this the work, which was ex- 

 ecuted within a short period of time, may be considered 

 as a success. 



Sheeting of the New North Harbour Dam at Harlingen 1947-48, 



IliSiES^l "'""" 



Quite a different kind of experiment with the application of 

 asphaltic bitumen on a large scale is found in the protection of 

 the new North harbour dam at Harlingen, where a dam consisting 

 of sand was simply covered with a layer of so-called bituminous 

 sand, that is a warm mixture of 5% asphaltic bitumen and 95$ 

 sea sand. This material was produced in the Netherlands for the 

 first time by the Research Laboratory of Royal Shell at Amsterdam 

 in the spring of 1947 at the road building section of the Dutch 

 Concrete Association Ltd. (Hollandsche Beton Ifaatschappy) at 

 Amsterdam. A small addition of asphaltic bitumen proved sufficient 

 to bind the sand-particles strongly. The 160 m test section of 

 the North harbour dam at Harlingen, which was built in the same 

 year, was protected to the low water level by a layer of bituminous 

 sand containing 5% asphaltic bitumen and 95% sea sand, 0.40 m 

 thick to +4.00 m N.A.P. and 0.25 m thick above that level. 



The under water slope protection on the sea side, which was 

 constructed as a bituminous mattress, crumbled after it had 

 been undermined as it did not have the required flexibility. 

 Therefore during 1948 the existing work was re-covered over about 

 100 m length with a layer of a richer mixture containing 16$ 

 asphaltic bitumen (40/50) and 84$ sea sand. 



In 1948 the 900 m harbour dam was completed (figures 10, 11 

 and 12). The 1947 method was used once more with the exception 

 that: 



36 



