「三合土」巨形石棺....
「三合土」係1840之後先發揚光大,傳到中國都要幾十年,大概1900年,同隻錶差不多....咁個墓坑嘅年分...
http://en.wikipedia.org/wiki/Concrete
The secret of concrete was lost for 13 centuries until 1756, when the British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. Portland cement was first used in concrete in the early 1840s.
