7.4
コンクリート中の総空隙
コンクリート内の総空隙には、ゲル水量、毛細管細孔、閉じ込められた空気が含まれます。セメント水和生成物内に保持されるゲル水と物理的に閉じ込められた水または吸着された水は、水和プロセスにとって重要です。完全な水和には、セメント 1 cm^3 の生成物に必要なスペースが 2 倍になると推定されます。毛細管…
ボイドの総体積にゲル水、毛細管細孔、および閉じ込められた空気が占める体積が含まれ、それぞれがコンクリート構造の全体的な多孔性に寄与するコンクリートの塊を考えてみましょう。
セメントの水和の産物であるゲルは、物理的に保持されるか、水和物の広範な表面積に吸着される固体物質と水で構成されています。この特定の水の量は、ゲル水の量です。
1立方インチの非水和セメントは、完全な水和時にその水和生成物のために約2立方インチのスペースを必要とすると推定されています。
毛細管細孔は、水和物によって占められていない水和セメントペースト内のスペースであり、これらの細孔は空であるか、水で満たされている可能性があります。
コンクリートを混合する過程で、セメントペースト内に空気が閉じ込められることがよくあります。
これらの閉じ込められた空隙は最大120ミルに達する可能性があり、これは毛細管空よりも大幅に大きく、コンクリートの強度に悪影響を与える可能性があります。
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Q1: What are the three main components that make up total voids in concrete?
Total voids in concrete consist of gel water, capillary pores, and entrapped air. Gel water is retained within cement hydration products through physical adsorption onto hydrate surfaces. Capillary pores are unoccupied spaces in the hydrated cement paste, while entrapped air becomes trapped during mixing and can reach up to 120 mils in size, substantially larger than capillary voids.
Q2: How much space is required for cement hydration products compared to unhydrated cement?
During complete hydration, approximately two cubic inches of space are needed for the hydration products of one cubic inch of unhydrated cement. This significant volume expansion occurs because the gel, which is the product of cement hydration, contains both solid substances and water physically retained or adsorbed onto the extensive surface area of the hydrates.
Q3: What is gel water and why is it important in concrete?
Gel water is the volume of water physically retained or adsorbed onto the extensive surface area of cement hydration products. This water is a key component of the gel formed during cement hydration and contributes to the overall porosity of the concrete structure. Understanding gel water volume is essential for assessing the hydration process and concrete performance.
Q4: How do capillary pores differ from entrapped air voids in concrete?
Capillary pores are small, irregularly shaped spaces within hydrated cement paste that range from nanometers to a few micrometers in diameter. Entrapped air voids, typically spherical, are substantially larger, reaching up to 120 mils. The distribution of capillary pores is considered a more precise indicator of hydrated cement paste characteristics than total porosity alone.
Q5: Why do entrapped air voids negatively impact concrete strength?
Entrapped air voids can reach up to 120 mils, making them substantially larger than capillary voids. These large voids reduce the effective load-bearing area and create stress concentration points within the concrete matrix. Understanding and controlling void volume and distribution is essential for optimizing concrete's strength and permeability properties.
Q6: What factors influence the size and distribution of capillary pores?
The size and distribution of capillary pores are largely influenced by the water-to-cement ratio and the degree of hydration. Lower water-to-cement ratios generally produce finer, more densely distributed capillary pores. The distribution of these capillary voids is believed to be a more precise indicator for assessing hydrated cement paste characteristics than total porosity.
Q7: How do voids affect both concrete strength and permeability?
Voids significantly impact concrete by affecting both strength and permeability. Larger entrapped air voids weaken the concrete structure, while capillary pores influence water penetration and durability. To optimize concrete's properties, controlling the volume and distribution of all void types is essential for achieving desired strength and resistance to environmental degradation.