In this study the boundary zone around polypropylene fibres in hardened cement paste was defined in terms of porosity and unhydrated cement particles using the phase contrast tomography with a spatial resolution of $0.637\mu \text{m}$ within a volume of $1.305\times 1.305\times 1.305{\text{ mm}}^3$. Pores and unhydrated grains were identified from the cement paste made of blended cement by separating them from computed tomography images using thresholding method. In the identification of the gray-level ranges of pores and unhydrated particles several approaches, such as tangent-slope and overflow criterion including the cumulative curve of the gray-level image, were utilised. The changes in relative amounts of pores and unhydrated particles indicated that the boundary zone extended to a distance of $70\mu \text{m}$ from the fibre surface. Within the boundary zone, the porosity was about twice or even four times higher than in the bulk cement paste. The volume fraction of pores was observed to vary from 7% to 35% close to the fibre, where the pores were also typically interconnected with the resolution used. Compared to bulk cement paste, the amount of pores exceeding a volume of ${10}^5\mu {\text{m}}^3$ increased in the boundary zone. Close to the fibre surface, the volume fraction of unhydrated particles was about 2% being 33% of the value outside the boundary zone.

在这项研究中，使用相差断层扫描技术以空间分辨率为1来定义硬化水泥浆中聚丙烯纤维周围的边界区域，以孔隙率和未水合水泥颗粒的形式定义。 $0.637\mu \text{米}$ 在...的范围内 $1.305\times 1.305\times 1.305{\text{ 毫米}}^3$。通过使用阈值法将其与计算机断层扫描图像分开，从混合水泥制成的水泥浆中识别出孔隙和未水合的颗粒。在确定孔隙和未水合颗粒的灰度范围时，采用了诸如切线斜率和溢出标准（包括灰度图像的累积曲线）之类的几种方法。孔隙和未水合颗粒的相对数量的变化表明边界区延伸到$70\mu \text{米}$从纤维表面。在边界区内，孔隙度比散装水泥浆高约两倍甚至四倍。观察到孔的体积分数在接近于纤维的7％至35％之间变化，其中，孔通常还与所使用的分辨率互连。与散装水泥浆相比，孔的数量超过了${10}^5\mu {\text{米}}^3$在边界区域增加。靠近纤维表面的未水合颗粒的体积分数约为2％，是边界区域外部值的33％。