low-quality aggregates

In some areas, excellent aggregates have been exploited and utilized, only low-quality aggregates left. Considering from construction economy, utilizing low-quality has been an inexorable trend .
優良的骨料在某些地區已經開發利用，賸下的是低品質骨料，從建築經濟上考慮，利用低品質骨料已成必然趨勢。