Cau 3:

Tinh luong dung vat lieu thuc te cho 1 me trong be tong Vm= 425 lit;

1m3 be tong theo thiet ke: X=312kg; N=182 lit; C=612kg; D=1296kg;

Wc=2%; Wd=0,5%; β =0,7;

Bai giai:

Ap dung cong thuc x= X.Vm.β/ 1000

ta co luong vat lieu dung cho 1 me trong cua may 425lit la:

x= 312.425.β/1000 =92,82(kg)

n= 182.425.β/1000 =54,23(lit)

c= 612.425.β/1000 =182(kg)

d= 1296.425.β/1000 =386(kg)

Khi vat lieu co am Wc=2%; Wd=0,5% thi

x’ =x =92,82(kg)

n’ =n -(c.Wc +d.Wd) =48,66(lit);

c’ =c.(1+Wc) =185,64(kg);

d’ =d.(1+Wd) =387,93(kg)

Cau 1: Bien dang la gi? The nao la bien dang deo va bien dang dan hoi (nguyen nhan va anh huong den kha nang su dung vat lieu)?

1/ Tinh bien dang cua VLXD la tinh chat buoc no co the thay doi hinh dang kich thuoc duoi su tac dong thuoc tai trong ben ngoai.

*/ Nguoi ta chia bien dang thanh 2 loai: bien dang deo va bien dang dan hoi

- Bien dang dan hoi la bien dang hoan toan mat di khi loai bo nguyen nhan gay bien dang

            + Bien dang dan hoi thuong xay ra khi tai trong tac dung be va ngan han.

- Bien dang deo la bien dang khong mat di khi loai bo nguyen nhan gay bien dang.

            + Bien dang deo xay ra khi ngoai luc tac dung lon hon noi luc

- Qua trinh la viec cua bien dang dan hoi tuan theo dinh luat Huc

E= δ/ε voi ε=∆l/l

δ: ung suat (kg/cm2);

ε: bien dang tuong doi.

Cau 2: Thoi gian ninh ket cua ximang Pooclang? Y nghia cua chi tieu thoi gian bat dau ninh ket va ket thuc ninh ket?

1/ Thoi gian ninh ket:

*/ K/n: Thoi gian ninh ket cua ximang duoc xac dinh tu ho^' deo tieu chuan bang dung cu vica (d=1mm);

thoi gian ninh ket chia lam 2 thoi ki

- Bat dau ninh ket la quang thoi gian ke tu khi do nuoc toi khi ho^' xi mang  het tinh deo, ung voi luc do kim vica cam sau 1÷2mm.

- Thoi gian ket thuc ninh ket: la quang thoi gian ke tu khi do nuoc cho den khi ho^1 ximang xuat hien cac tinh the co cuong do ung voi luc do kim vica cam sau vao mat ho^' la 1÷2mm

*/ Phuong phap xac dinh: phuong phap thu da^'n: d= 1±0,1mm

- Lay 400g ximang, lay luong nuoc tieu chuan thuoc ximang

- Lay tay chao bang gie a^’m

- Do ximang vao, tao thanh lo nho, do nuoc tron deu.

- Xuc 1 lan do vao khuon, tao chan dong, cat bang mat, dat kim vica vao

- Sau 45p tha kim, sau do 5p lai tha kim 1 lan.

*/ Cac yeu to anh huong:

+ Thanh phan hoa hoc: CaO lam cho ximang ran nhanh; CaSO; H2O co tac dung dieu chinh thoi gian ninh ket cho ximang. Ngoai ra cac chat photphatnitrat canxi, natri, nhom, duo'ng la nhung chat lam chat cham ninh ket. Cacbonat va clorua thuoc kim loai mem la nhung chat lam tang nhanh ninh ket.

+ Thanh phan khoang vat: C3S, C3A: la nhung thanh phan lam cho xi mang ran nhanh; giam thoi gian ninh ket.

+ Do min: tang do min cua ximang co nghia la tang do thu?y ho’a, giam thoi gian ninh ket.

+ Thoi tiet, khi hau: do am, nhiet do thuoc moi truong co anh huong den qua trinh ran chac cua da ximang vi' giai doan dau thuoc qua trinh ran chac la thuy hoa. Neu moi truong a^?m tao dieu kien de tang toc do thu?y hoa. Toc do cua cac phan ung giua cac khoang clanke voi nuoc tang len voi su tang nhiet do → thoi gian ninh ket giam

2/ Y nghia

- khi xi mang bat dau ninh ket no’ mat tinh deo, do do’ khoang thoi gian nay phai du? de^? thi cong, thoi gian ninh ket cang cham thi cang de thi cong. Theo TCVN thoi gian bat dau ninh ket ≥45’

- Thoi gian ninh ket xong la luc ximang dat duoc cuong do nhat dinh, thoi gian nay phai du ngan de co the thi cong nhanh, yeu cau ko duoc vuot qua 10h