motar 和 concrete...的問題~~help~

1. Mortar 當然唔同 concrete。　mortar 係由 cement, lime and sand 組成，　ratio of content 係1:1:6。　而concrete係由sand, gravel，water同埋 cement　組成。　而water / cement ratio會影響 concrete 既強度，　簡單Ｄ黎講，　water/cement ratio　同　concrete 強度係成反比例。　concrete係一種建築材料，　由於本身weak in tension，　所以都會加d steel bar係入面，　而呢樣野就係reinforced concrete。Mortar只係用作填補磚頭（brick）同磚頭之間之空隙。

２。　由於mortar係用作填補磚頭同磚頭之間之空隙，　當一塊磚牆受壓時，　for example compression in vertical direction，　呢2種material（mortar and brick）都會受到相同壓力。 由於Poission Effect，　所以vertical compression會造成horizontal tension。　加上由於呢2種 material 有唔同Yield strength, strian, i.e.elongation, 都會唔同。　Mortar由於係weaker than brick，　佢既elongation會大d，　而difference of elongation between these 2 materials 會 induce 一個 internal shear stress， 呢個shear stress 會O係 brick入面造成裂痕。 所以係呢個情況下， 塊牆唔可以承受太強既compression， 因為過多既compression會引起過大horizontal tension， 繼而過大elongation difference 會造成過大internal shear stress。 而要解決呢個問題， 就要加non-shrink agent係mortar入面。