4() ANNUAL REPORT 
surface where it is composed of a mortar too rich in cement. In some 
cases this effect has been particularly aggravated by troweling more 
cement to the surface. The neat cement film has a different coefficient of 
contraction than the mortar of sand and cement and causes fine cracks on 
the surface in setting. This effect is seldom seen in surfaces where 
coarse sand has been used. One very successful walk builder in Peoria, 
Illinois, said that while specifications usually called for a top coat of I 
cement to 1 sand, he could do better work with a mortar of I cement to 
1% or 2 sand, usually using a 1 to 14% mortar. He has the reputation of 
being one of the safest and best walk builders in Central Illinois. 
In and around Chicago the specifications for cement walks usually call 
for the top coating to be of one part Portland cement and one part of 
clean coarse sand or torpedo gravel, which is a fine uniform gravel, slightly 
coarser than the standard crushed quartz used in cement laboratory tests. 
The walks, as a rule, around Chicago, are durable, well made walks, and 
seldom show veins or sun cracks. 
The concrete walks in the Ohio State University campus show veins 
in many places and the writer has been watching their development for 
over two years. At first, fine hair-cracks appeared upon the surface of the 
walks, then after some time a deposit of brownish or slate colored material 
appeared along the hair-cracks and the cracks were more marked, became 
wider and more continuous. The deposit became from % to % inch in 
width and of appreciable thickness. After two or more years the cracks 
open much more rapidly, as the frost seems to obtain better leverage. 
Samples of this brown deposit were analyzed for the writer by Mr. 
A. V. Bleininger, chemist in the Department of Ceramics, with the follow- 
ing results: | 
Per cents. 
Soluble: Matter 25. ehc 2 ck A enna ke EPR Nee 7.61 
SUT Ca se eee ca katie 2a TR Pte SOT OIE ae CANE Re ane 33 .06 
7 Cib 6 oan h 0: haserigetees MOO iman pieen ec eMed Sem cre MIu maa SMe Riri Sebo 3.68 
CalELUmMeEOK Me cis Ee oe Resa tener Np REY eet ea a 37.98 
Maenesium: Oxide sok te ono ree eae oe tees 7.02 
Losses, black organic matter—sulphur, alkalies, etc....10.65 
T Ota Li esi ce ed er erm aan oe Ca On OA ee Ae 100.00 
The soluble matter analyzed as follows: 
3 Per cents. 
ACTUATE Sis Eee eile at ap ar oe EO 1.07 
Caletiuim, Oxide iSO 8 BE RR eee eee 1.84 
Maenesium Oxide. wean stole son ene ero 0.06 
ATK ali esi) CU Gal re POEs Tree ria a ens aera pra anita teaee eat 4.64 
Woy v2 W Maer RUT STOLE MU Ura OS Se ead ola a ores 7.61 
The mortar in the concrete next the veins was analyzed and showed, 
Per cents. 
MaenesiumuOxide oasis acer iterele encot rer aiererariens Ibs 
Sulphuric? Anhydridemreaacae nici clei ere nerreienn. 1.53 
