B rid ges ▁in ▁South ▁Dak ota ▁Category : National ▁Register ▁of ▁Historic ▁Places ▁in ▁South ▁Dak ota ▁Category : Build ings ▁and ▁structures ▁completed ▁in ▁ 1 9 1 2 ▁Category : San born ▁County , ▁South ▁Dak ota <0x0A> </s> ▁Fo am ▁glass ▁gra vel ▁is ▁a ▁building ▁material ▁made ▁from ▁rec yc led ▁glass . ▁ ▁Character istics ▁ ▁Fo am ▁glass ▁gra vel ▁is ▁light ▁and ▁dimension ally ▁stable ▁with ▁a ▁lambda ▁rating ▁of ▁ 0 . 0 8 ▁W / m K ▁and ▁a ▁specific ▁weight ▁of ▁ 1 5 0   kg ▁per ▁cub ic ▁met re . ▁Being ▁made ▁from ▁glass , ▁the ▁aggregate ▁is ▁non - comb ust ive ▁and ▁in ert , ▁age ing ▁resist ant , ▁p H ▁neutral ▁and ▁insect ▁and ▁rod ent ▁resist ant . ▁The ▁manufact uring ▁process ▁se als ▁the ▁air ▁b ub bles ▁giving ▁the ▁gra vel ▁non - cap ill ary ▁properties . ▁The ▁material ▁has ▁a ▁high ▁compress ive ▁strength ▁as ▁well ▁as ▁ins ul atory ▁properties ▁making ▁it ▁ideal ▁for ▁ins ulated ▁floor ▁construction ▁ ▁S our cing ▁and ▁manufact ure ▁ ▁G lass ▁sh ards ▁are ▁clean ed ▁and ▁mil led ▁to ▁a ▁pow der ▁before ▁a ▁fo aming ▁agent , ▁active ▁carbon , ▁is ▁added ▁in ▁either ▁liquid ▁or ▁solid ▁form . ▁The ▁material ▁is ▁passed ▁through ▁a ▁continuous ▁tunnel ▁furn ace ▁and ▁he ated ▁to ▁a ▁temperature ▁of ▁ 8 0 0 – 9 0 0   ° C . ▁Opt imum